Seasonal changes in the endocrine responsiveness of the pituitary and testes of male sheep in relation to their patterns of gonadotropic hormone and testosterone secretion

1984 ◽  
Vol 62 (7) ◽  
pp. 827-833 ◽  
Author(s):  
L. M. Sanford ◽  
B. E. Howland ◽  
W. M. Palmer
Keyword(s):  
Seasonal Changes ◽  
Testis Size ◽  
Gonadotropic Hormone ◽  
Testosterone Levels ◽  
Testosterone Secretion ◽  
Testicular Regression ◽  
Serum Hormone ◽  
Lh Release ◽  
Circulating Levels ◽  
Male Sheep

Pituitary and testicular endocrine responses to exogenous gonadotropin releasing hormone (GnRH) and luteinizing hormone (LH), respectively, were assessed for adult rams in an investigation of the regulation of seasonal changes in the patterns of episodic LH and testosterone secretion. Concurrent variations in testis size and in circulating levels of follicle stimulating hormone (FSH) and prolactin (PRL) were also examined. On 10 occasions throughout the year, serum hormone levels were assessed over 6- to 8-h periods during which time rams were left untreated (day 1) or were injected (iv) with single doses of either 10 μg synthetic GnRH (day 2) or 30 μg NIH-LH-S18 (day 3); blood samples were collected from the jugular vein at 10- or 20-min intervals. Testicular redevelopment during the summer, as indicated by increasing testis diameter measurements, was associated with increases in mean FSH level and was preceded by a springtime rise in mean PRL level; "spontaneously" occurring LH pulses and those produced in response to GnRH treatment were relatively large during this period. Increases in the magnitude of testosterone elevations in response to both endogenously and exogenously produced LH pulses occurred in August. Mean testosterone levels were elevated fourfold in the fall as a consequence of relatively frequent and small LH pulses stimulating a more responsive testis to produce more frequent and larger testosterone elevations; endogenous LH pulses, however, did not appear to stimulate the testes maximally at this time. Testicular regression occurred during the winter months and was characterized initially by decreases in testosterone levels without obvious changes in the pattern of pulsatile LH release and subsequently by a decrease in testicular responsiveness to relatively infrequent LH pulses which led to further decreases in testosterone levels and smaller testes. Results demonstrate that alterations in pituitary and testicular responsiveness to stimulatory hormones account in part for seasonal changes in the magnitude of LH and testosterone secretory pulses in adult rams.

INFLUENCE OF AGE AND BREED ON CIRCULATING LH, FSH AND TESTOSTERONE LEVELS IN THE RAM

1982 ◽  
Vol 62 (3) ◽  
pp. 767-776 ◽  
Author(s):  
L. M. SANFORD ◽  
W. M. PALMER ◽  
B. E. HOWLAND
Keyword(s):  
Jugular Vein ◽  
Age Groups ◽  
Reproductive Hormone ◽  
Testosterone Levels ◽  
Breed Differences ◽  
Serum Hormone ◽  
Key Words Age ◽  
Lh Release ◽  
The Mean ◽  
Circulating Levels

Possible age and breed differences in circulating levels of luteinizing hormone (LH), follicle stimulating hormone (FSH) and testosterone in the ram were investigated. In exp. 1, blood was collected from a group of 28 rams of various ages and breeds by venepuncture from the jugular vein at 20-min intervals for an 8-h period (May). Comparison of mean serum hormone concentrations for postpubertal Finnish Landrace (Finn), Suffolk and Managra Synthetic (Line M) rams did not reveal significant (P > 0.10) breed differences. However, when rams of the three breeds were categorized by age, the mean (±SE) LH levels in lambs (n = 8), yearling (n = 12) and adult (n = 8) animals were 2.1 ± 0.4, 1.1 ± 0.2 and 0.5 ± 0.1 ng/mL, respectively; the significant decrease (P < 0.05) in LH levels in adult vs. yearling rams was due to fewer and smaller LH releases. Mean testosterone levels averaged 1.3 ± 0.2, 2.8 ± 0.4 and 2.4 ± 0.3 ng/mL for the lamb, yearling and adult ram groups, respectively. FSH levels were similar for all age groups. In exp. 2, a series of blood samples were collected from 3-mo-old Finn (n = 6) and Suffolk/Line-M crossbred (n = 6) rams in October. In comparison with crossbred rams, rams of the more prolific Finn breed exhibited substantially higher mean levels of LH (1.0 ± 0.2 vs. 0.4 ± 0.2 ng/mL; P < 0.10), FSH (250 ± 26 vs. 121 ± 16 ng/mL; P < 0.01) and testosterone (2.8 ± 0.9 vs. 0.4 ± 0.1 ng/mL; P < 0.05); higher LH and testosterone in Finn rams were associated with larger and/or more frequent elevations in the level of these hormones during the 8-h bleeding period. Results of this study seem to indicate (1) age-associated differences in the pattern of LH release in adult rams in the spring; and (2) that breed differences in blood reproductive hormone levels in postpubertal rams are not significant in the spring, but levels in 3-mo-old rams differ during the fall months according to genotype. Key words: Age, breed, gonadotropins, testosterone, serum, ram

Maintaining a high physiological rate of testosterone secretion in the adult ram by estradiol immunoneutralization partially prevents testicular regression

1991 ◽  
Vol 71 (4) ◽  
pp. 1099-1109 ◽  
Author(s):  
Lee M. Sanford ◽  
Donna G. Leggee ◽  
Peter M. Melnyk
Keyword(s):  
Pulse Amplitude ◽  
Base Line ◽  
Testis Size ◽  
Testosterone Secretion ◽  
Scrotal Circumference ◽  
Testicular Regression ◽  
Testicular Recrudescence ◽  
Hypothalamic Pituitary Axis ◽  
A Minor ◽  
Sperm Output

The seasonal testicular cycle of 10 adult Dorset × Leicester × Suffolk rams was entrained to alternating 4-mo periods of long-inhibitory (16 h light) and short-stimulatory (8 h light) day lengths. Beginning in the third month of a short-day period, when the testes were fully redeveloped, five rams were passively immunized with a low titre (1:200) of estradiol antiserum for 13 wk. During this time the testes of the remaining (control) rams regressed almost completely. Estradiol immunoneutralization reliably maintained most characteristics of testosterone secretion (mean and base-line concentrations, and pulse amplitude) at "breeding season" values and had a minor but persistent effect on the hypothalamic–pituitary axis. When both the immunization period and the following 6 mo were considered, LH pulses were 50% larger in the immunized rams than in the control rams. Testicular regression was partially prevented in the immunized rams. However, their 1.5- to 1.7-cm larger scrotal circumference during most of the regression stage was not associated with a greater daily sperm output (based on sperm voided in urine) early in the redevelopment stage. Mean LH and FSH concentrations were increased by 200% in all rams during testicular recrudescence, and maximum testis size was achieved 1 mo earlier in the immunized rams than in the control rams. Immunization of rams against estradiol effectively maintained a high physiological rate of testosterone secretion, but was not able to prevent the normal decline in quantitative spermatogenesis. Key words: Estradiol immunoneutralization, testicular regression, testosterone, adult ram

Seasonal changes in the plasma testosterone profile in Merino rams

1983 ◽  
Vol 23 (122) ◽  
pp. 254 ◽  
Author(s):  
MJ D'Occhio ◽  
DE Brooks
Keyword(s):  
Seasonal Changes ◽  
Mating Behaviour ◽  
Point Of View ◽  
Plasma Testosterone ◽  
Seasonal Trends ◽  
Testosterone Levels ◽  
Testosterone Secretion

The pattern of testosterone secretion (i.e. profile of plasma testosterone sampled every hour for 24 h) was characterized for Merino rams at various times during the year at latitude 35�S to assess seasonal trends. The profiles of plasma testosterone were always characterized by random peaks regardless of season. However, at any particular time of the year, there were large differences between individual rams in the number of peaks124 h (range 1-7). Mean plasma testosterone levels were higher and a greater number of peaks were recorded per 24 h in summer (December-January) than in winter (July) and spring (September-October). Seasonal changes observed in the plasma testosterone profile of Merino rams were consistent with the concept that activity of the hypothalamic-pituitary-gonadal axis in sheep is entrained to changes in the photoperiod. Merino rams at latitude 35�S are therefore markedly seasonal from an endocrine point of view, although they are not generally regarded as seasonal breeders based on mating behaviour.

Androgenic and oestrogenic steroid participation in feedback control of luteinizing hormone secretion in male sheep

1983 ◽  
Vol 102 (4) ◽  
pp. 499-504 ◽  
Author(s):  
M. J. D'Occhio ◽  
B. D. Schanbacher ◽  
J. E. Kinder
Keyword(s):  
Luteinizing Hormone ◽  
Pulse Generator ◽  
Hormone Secretion ◽  
Pulse Interval ◽  
Serum Concentrations ◽  
Luteinizing Hormone Secretion ◽  
Lh Release ◽  
Lh Secretion ◽  
Additional Feedback ◽  
Male Sheep

Abstract. The acute castrate ram (wether) was used as an experimental model to investigate the site(s) of feedback on luteinizing hormone (LH) by testosterone, dihydrotestosterone and oestradiol. At the time of castration, wethers were implanted subdermally with Silastic capsules containing either crystalline testosterone (three 30 cm capsules), dihydrotestosterone (five 30 cm capsules) or oestradiol (one 6.5 cm capsule). Blood samples were taken at 10 min intervals for 6 h 2 weeks after implantation to determine serum steroid concentrations and to characterize the patterns of LH secretion. Pituitary LH response to exogenous LRH (5 ng/kg body weight) were also determined at the same time. The steroid implants produced serum concentrations of the respective hormones which were either one-third (testosterone) or two-to-four times (dihydrotestosterone, oestradiol) the levels measured in rams at the time of castration. Non-implanted wethers showed rhythmic pulses of LH (pulse interval 40–60 min) and had elevated LH levels (16.1 ± 1.6 ng/ml; mean ± se) 2 weeks after castration. All three steroids suppressed pulsatile LH release and reduced mean LH levels (to below 3 ng/ml) and pituitary LH responses to LRH. Inhibition of pulsatile LH secretion by all three steroids indicated that testosterone as well as its androgenic and oestrogenic metabolites can inhibit the LRH pulse generator in the hypothalamus. Additional feedback on the pituitary was indicated by the dampened LH responses to exogenous LRH.

RELATIONSHIP BETWEEN BLOOD LEVELS OF LUTEINIZING HORMONE AND TESTOSTERONE IN BULLS, AND THE EFFECTS OF SEXUAL STIMULATION

1971 ◽  
Vol 50 (3) ◽  
pp. 457-466 ◽  
Author(s):  
C. B. KATONGOLE ◽  
F. NAFTOLIN ◽  
R. V. SHORT
Keyword(s):  
Luteinizing Hormone ◽  
Immediate Release ◽  
Blood Levels ◽  
Testosterone Levels ◽  
Peripheral Plasma ◽  
Sexual Stimulation ◽  
Maximal Stimulation ◽  
Cyclical Pattern ◽  
Lh Release ◽  
Competitive Protein Binding

SUMMARY Luteinizing hormone (LH) and testosterone were measured in the peripheral plasma of two bulls by radioimmunoassay and competitive protein binding techniques. Samples were collected from an indwelling jugular catheter once an hour for 24 h, and then at more frequent intervals after a number of experimental procedures. Each bull showed its own characteristic pattern of cyclic LH changes, with 5–10 peaks during 24 h that were apparently unrelated to daylight, feeding or sleep. Each LH peak was associated with a testosterone peak; the LH concentrations ranged from 5 to 50 ng/ml, and those of testosterone from 2 to 20 ng/ml. Sexual stimulation, such as the sight of a cow, or 'teasing', or on one occasion the act of ejaculation itself, caused an immediate release of a large amount of LH. If the testosterone levels were low at the time, the LH peak was followed by a testosterone peak. But when the testosterone levels were high at the time of LH discharge, the testis seemed to be unable to respond any further. An intravenous injection of 500 i.u. human chorionic gonadotrophin was associated with LH release and caused the testosterone levels to rise to maximal values of 22 ng/ml within 1½ h. It is concluded that the cyclical pattern of LH release is due to some inherent central rhythm, and that each transient LH peak results in transient maximal stimulation of testicular testosterone secretion.

Increases in testosterone secretion in adult rams with immunoneutralization of endogenous estradiol occur in the absence of increases in pulsatile LH release or testicular LH receptors

1989 ◽  
Vol 120 (2) ◽  
pp. 180-186 ◽  
Author(s):  
Lee M. Sanford
Keyword(s):  
Binding Sites ◽  
Cell Function ◽  
Passive Immunization ◽  
Serum Testosterone ◽  
Experimental Period ◽  
Pulse Amplitude ◽  
Testicular Biopsy ◽  
Binding Activity ◽  
Testosterone Secretion ◽  
Lh Release

Abstract. The testes of the ram become more responsive to LH stimulation following immunoneutralization of endogenous estradiol. The possibility that testosterone secretion is facilitated by increased LH-binding activity in the testes was investigated in the present study conducted with adult Dorset × Leicester × Suffolk rams during the time of testicular recrudescence. Patterns of episodic LH release and testosterone secretion (days –5, 10 and 24) and LH-binding activity in testicular biopsy samples (days –1, 14 and 28) were assessed on the days indicated relative to the onset of passive immunization and the establishment of relatively low titres (~1:200) of estradiol antiserum. During the experimental period, mean serum testosterone concentration increased by approximately 150% for the immunized rams as basal concentration and pulse amplitude increased, while all characteristics of testosterone secretion remained unchanged for the nonimmunized rams. Characteristics of LH release and the concentration of LH-binding sites in the testes, however, were always similar for both groups of rams. Further, group differences in FSH and PRL secretion and in the concentration of testicular FSH-binding sites did not occur. These results provide evidence for an estradiol direct (gonadotropin independent) negativefeedback component in the regulation of Leydig cell function in the ram.

Reproductive hormone secretion and spermatogenic function in thyroidectomized rams receiving graded doses of exogenous thyroxine

1986 ◽  
Vol 111 (2) ◽  
pp. 245-253 ◽  
Author(s):  
Y. Chandrasekhar ◽  
M. J. D'Occhio ◽  
B. P. Setchell
Keyword(s):  
Hormone Secretion ◽  
Reproductive Function ◽  
Pulse Frequency ◽  
Endocrine Function ◽  
Sex Hormone Binding Globulin ◽  
Testosterone Levels ◽  
Reproductive Endocrine ◽  
Lh Release ◽  
Lh Releasing Hormone ◽  
The Relationship

ABSTRACT This study aimed to obtain a better understanding of the relationship between circulating thyroxine (T4) concentrations and reproductive endocrine function in the ram. Mature Merino rams were thyroidectomized and supplemented with 0, 30, 100 and 300% of normal T4 for 10 weeks. Thyroidectomy had no apparent effect on spermatogenic function but interfered with sperm maturation, the latter being returned to normal by 30% T4 replacement. Circulating testosterone levels were reduced by thyroidectomy and restored to control levels by 30% T4; when T4 levels were supranormal (300%), circulating testosterone levels were again reduced. The lowered circulating testosterone levels in thyroidectomized rams occurred as a result of suppressed testosterone secretion from the testis, observed under basal conditions and also following LH-releasing hormone (LHRH) and human chorionic gonadotrophin injection. In thyroidectomized rams, sex hormone binding globulin (SHBG) levels were depressed without changes in testosterone clearance rate (TCR), while in rams with supranormal T4 levels, TCR was increased without changes in SHBG levels. Subnormal levels of T4 also restored to normal the reduced LH pulse frequency in thyroidectomized rams. Reduced LH pulse frequency, together with diminished LH release following LHRH injection in thyroidectomized rams, suggested effects of T4 at the hypothalamo-pituitary axis. The present study demonstrates that complete lack of thyroid hormones suppresses normal reproductive endocrine function in the ram, but that this can be restored to normal by 30% T4 replacement. The results support the theory that T4 plays a permissive rather than a regulatory role in reproductive function in males. J. Endocr. (1986) 111, 245–253

scholarly journals The relationship between serum hormone levels (follicle-stimulating hormone, luteinizing hormone, total testosterone) and semen parameters

2015 ◽  
Vol 87 (3) ◽  
pp. 194 ◽  
Author(s):  
Mehmet Zeynel Keskin ◽  
Salih Budak ◽  
Tuǧba Zeyrek ◽  
Orçun Çelik ◽  
Oguz Mertoglu ◽  
...  
Keyword(s):  
Sperm Concentration ◽  
Reference Value ◽  
Semen Parameters ◽  
Total Testosterone ◽  
Testosterone Levels ◽  
Progressive Motility ◽  
Semen Volume ◽  
Significant Difference ◽  
Serum Hormone ◽  
Serum Gonadotropin

Objective: The aim of this study was to investigate the effect of serum gonadotropin and total testosterone levels on semen parameters. Materials and Methods: Three hundred and eighty-two patients that applied to a male infertility polyclinic were included in our study. Serum gonadotropin and total testosterone levels and semen parameters of the patients were analyzed during the first visit to the clinic. The reference FSH value was 1.5-12.4 mIU/mL, that of LH was 1.7-8.6 mIU/mL and the reference value for total testosterone was 249-836 ng/dL. Results: While there was no statistically significant difference between the patients with low gonadotropin levels and the controls regarding any of the semen parameters (p &gt; 0.05), there was a strong statistically significant difference between the patients with high gonadotropin levels and the controls regarding sperm concentration (p = 0.000), total motility (p = 0.000), progressive motility (p = 0.000), and morphology (p = 0.000). There was a strong statistically significant difference between the patients with low testosterone levels and the controls regarding total motility (p = 0.012) and progressive motility (p = 0.010), and a weak statistically significant difference in morphology (p = 0.042). There was no statistically significant difference in semen volume or sperm concentration (p &gt; 0.05). There was no statistically significant difference in any of the semen parameters between the patients with high testosterone levels and the controls (p &gt; 0.05). Conclusions: Our findings especially regarding LH and T levels are not in agreement with previous reports. In this regard, there is a need for larger-scale and randomized trials to resolve this discrepancy.

scholarly journals Prolactin regulation of testosterone secretion and testes growth in DLS rams at the onset of seasonal testicular recrudescence

Reproduction ◽  
2010 ◽  
Vol 139 (1) ◽  
pp. 197-207 ◽  
Author(s):  
L M Sanford ◽  
S J Baker
Keyword(s):  
Peripheral Blood ◽  
Entire Period ◽  
Testosterone Levels ◽  
Testosterone Secretion ◽  
Testicular Recrudescence ◽  
The Times ◽  
Transition Stages

Our objective was to test the hypothesis that prolactin (PRL) acts at both the pituitary and testis levels to regulate testosterone secretion in the adult ram. The focus was on the mid-regression to mid-redevelopment stages of a photoperiod-condensed ‘seasonal’ testicular cycle. DLS rams (six per group) were given daily s.c. injections of bromocriptine (4 mg) or vehicle during the entire period. Serum PRL concentration in control rams peaked at 103.4±22.1 ng/ml in late regression and then steadily declined (P<0.01) to 19.5±4.3 ng/ml, whereas PRL in treated rams was always ≤4.0 ng/ml. Suppression of PRL tended (P<0.10) to increase the amplitude of natural LH pulses (transition stages) or reduce the number of LH receptors in the testis (regressed stage), although neither change disturbed testosterone levels in peripheral blood. These subtle changes were accompanied by significant (P<0.05) alterations in the capability of the pituitary to release LH (85% more) and of the testes to secrete testosterone (20% less). These effects of PRL were unmasked when rams were given highly stimulative i.v. injections of GNRH (single 3 μg dose) and NIH-oLH-S24 (three 5 μg doses given 20 min apart) respectively. PRL insufficiency also appeared to slow down the ‘seasonal’ rise in FSH secretion and slightly delayed (2 weeks) the times when the testes began to grow and were first significantly (P<0.05) enlarged from the regressed state. We conclude that PRL is an important part of the intricate regulation of the pituitary–gonadal system in moderately seasonal DLS rams.

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