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

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.

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LEVELS OF FOLLICLE-STIMULATING HORMONE, LUTEINIZING HORMONE, OESTRADIOL-17β AND PROGESTERONE, AND FOLLICULAR GROWTH IN THE PSEUDOPREGNANT RAT

Journal of Endocrinology ◽

10.1677/joe.0.0640037 ◽

1975 ◽

Vol 64 (1) ◽

pp. 37-47 ◽

Cited By ~ 86

Author(s):

R. WELSCHEN ◽

P. OSMAN ◽

J. DULLAART ◽

W. J. DE GREEF ◽

J. TH. J. UILENBROEK ◽

...

Keyword(s):

Luteinizing Hormone ◽

Follicle Stimulating Hormone ◽

Blood Levels ◽

Normal Cycle ◽

Antral Follicles ◽

A Value ◽

Wide Range ◽

Lh Release ◽

Competitive Protein Binding ◽

Stimulating Hormone

SUMMARY Throughout a period of pseudopregnancy the peripheral blood levels of progesterone, oestradiol-17β, follicle-stimulating hormone (FSH) and luteinizing hormone (LH), as well as the size-distribution of ovarian antral follicles were estimated in the rat. The progesterone concentrations, as measured by a competitive protein-binding technique, exceeded metoestrous values (25 ng/ml plasma) from day 3 of pseudopregnancy onwards. The highest levels were found on days 6 and 8 (91 ng/ml). From day 8 onwards the levels decreased gradually but were still above metoestrous values on the day of pro-oestrus after pseudopregnancy. Concentrations of oestradiol-17β, as measured by radioimmunoassay, were within the range of those at metoestrus (about 5 pg/ml plasma) until day 10. Thereafter levels increased to a value of 57 pg/ml. Concentrations of FSH, measured by radioimmunoassay, were within the range of metoestrous values until day 10 (about 100 ng NIAMD-rat-FSH RP-1/ml serum), but declined to a level of 33 ng/ml on day 12. Concentrations of LH, measured by radioimmunoassay, were generally within the wide range of metoestrous values (9–60 ng NIAMD-rat-LH RP-1/ml serum), but concentrations found on days 4, 8 and 10 were significantly lower than those found on preceding or subsequent days. Histological determination of the number of follicles present in various volume-classes, showed an increase in antral follicles on days 1 and 2, comparable to the increase observed during metoestrus and dioestrus 1 of the normal cycle. There was no change in the follicles between days 3 and 10 and they resembled those of early dioestrus. Preovulatory growth had occurred by day 12. Injection of human chorionic gonadotrophin (HCG) on days 2, 4 or 6 showed that ovulation could be induced only in some of the larger follicles. On the basis of these results it is suggested that during pseudopregnancy the high progesterone levels present result in a decreased plasma LH level which is insufficient to cause full maturation of the follicles and to stimulate oestrogen secretion to the levels required for induction of an ovulatory surge of LH release.

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SEASONAL VARIATIONS IN BLOOD LUTEINIZING HORMONE AND TESTOSTERONE LEVELS IN RAMS

Journal of Endocrinology ◽

10.1677/joe.0.0600101 ◽

1974 ◽

Vol 60 (1) ◽

pp. 101-106 ◽

Cited By ~ 58

Author(s):

C. B. KATONGOLE ◽

F. NAFTOLIN ◽

R. V. SHORT

Keyword(s):

Luteinizing Hormone ◽

Seasonal Changes ◽

Binding Assay ◽

Endocrine Activity ◽

Blood Samples ◽

Testosterone Levels ◽

Protein Binding Assay ◽

Competitive Protein Binding Assay ◽

Competitive Protein Binding ◽

Lh Secretion

SUMMARY Three adult Suffolk rams were bled at weekly intervals for 14 months, and at hourly intervals for 24 h during the summer (one ram) and autumn (two rams). Luteinizing hormone (LH) was measured by radioimmunoassay, and testosterone by a competitive protein binding assay. There were episodic bursts of LH secretion during the 24 h period in both the summer and the autumn; the frequency of discharge was lower in the summer, but the amplitude (0·1–8·0 ng/ml) did not appear to change. It was not always possible to detect seasonal changes in LH concentration in single blood samples taken once a week throughout the year. The blood testosterone levels also showed marked fluctuations throughout the 24 h, and the frequency of the peaks was lower in the summer. But in contrast to LH, the magnitude of the testosterone peaks also changed throughout the year; from January to September the testosterone concentration ranged from 0·5 to 10 ng/ml plasma, whereas from October to December it ranged from 3 to 28 ng/ml. Thus in temperate regions the ram, like the ewe, shows seasonal changes in gonadal endocrine activity, although some degree of spermatogenesis continues throughout the whole year.

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EFFECTS OF GnRH ON LUTEINIZING HORMONE RELEASE AND ONSET OF CYCLIC OVARIAN ACTIVITY POSTPARTUM IN PELIBUEY EWES

Canadian Journal of Animal Science ◽

10.4141/cjas88-041 ◽

1988 ◽

Vol 68 (2) ◽

pp. 359-366 ◽

Cited By ~ 2

Author(s):

A. GONZALEZ R. ◽

B. D. MURPHY

Keyword(s):

Luteinizing Hormone ◽

Key Words ◽

Luteal Phase ◽

Gonadotropin Releasing Hormone ◽

Ovarian Activity ◽

Hormone Release ◽

Similar Magnitude ◽

Hair Sheep ◽

Peripheral Plasma ◽

Lh Release

Synthetic gonadotropin releasing hormone (GnRH) was administered to Pelibuey ewes to determine its effect on luteinizing hormone (LH) release and on cyclic ovarian activity during the first 3 – 4 wk postpartum. Two GnRH doses were given (10 and 100 μg) on days 4 and 5, 7 and 8, 14 and 15, and 21 and 22, after parturition, respectively. In three trials, 11, 8 and 7 ewes were used. For each trial 5, 3 and 2 ewes were used as controls, respectively; in trial 3, only the 100-μg dose was given once. Results from the three trials indicated that LH release always occurred after GnRH treatment, relative to the saline-treated controls. In trials 1 and 2, the 10-μg dose induced a higher (P < 0.001) LH release than the 100-μg dose; the LH release in response to the 100-μg dose in the three trials was of similar magnitude. Release of LH in response to both doses was lower (P < 0.05) during days 4 – 5 postpartum, than during the following 3 wk. Two types of luteal activity or steroidogenesis were observed in the GnRH-treated ewes, relative to the saline-treated ewes; (1) within 2 – 4 d after each GnRH injection small peaks of progesterone appeared, and (2) within 5 – 15 d after the last GnRH injection there were elevations of progesterone in peripheral plasma to concentrations and of durations characteristic of the luteal phase of the ovine estrous cycle. These results indicate that the pituitary of postpartum Pelibuey ewes regains the ability for maximal release of LH in response to GnRH challenge within 7 d postpartum. Further, treatment with GnRH induces earlier return to cyclic ovarian activity. Key words: Hair sheep, postpartum, GnRH, luteal activity

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EFFECTS OF PROGESTERONE AND SYNTHETIC LUTEINIZING HORMONE RELEASING HORMONE ON THE RELEASE OF LUTEINIZING HORMONE DURING SEXUAL MATURATION IN THE HEN (GALLUS DOMESTICUS)

Journal of Endocrinology ◽

10.1677/joe.0.0670359 ◽

1975 ◽

Vol 67 (3) ◽

pp. 359-369 ◽

Cited By ~ 39

Author(s):

SUSAN C. WILSON ◽

P. J. SHARP

Keyword(s):

Luteinizing Hormone ◽

Sexual Maturation ◽

Feedback Mechanism ◽

Blood Levels ◽

Prolonged Release ◽

Incremental Change ◽

Basal Plasma ◽

Lh Release ◽

Positive Feedback Mechanism ◽

Lh Rh

SUMMARY Single intramuscular injections of 0·5 mg progesterone/kg resulted in increased LH secretion in laying hens but not in pullets with completely undeveloped sexual organs. Injections of the steroid were first able to stimulate LH release 8–10 weeks before the onset of lay when the comb, ovary and oviduct had started to grow and basal plasma LH concentrations were beginning to rise. At this time, injections of 10 μg synthetic LH-RH/kg resulted in an incremental change in plasma LH levels of around 26 ng/ml. A similar incremental change was observed after giving the same dose of LH-RH to pullets with no signs of sexual development. Three to four weeks before the first eggs were laid, basal plasma LH levels started to fall, the pituitary became progressively more insensitive to synthetic LH-RH and injections of 0·5 mg progesterone/kg resulted in a reduced LH response. Ten μg LH-RH/kg caused incremental changes in blood levels of LH of less than 5 ng/ml. The final stage of sexual maturation occurred during the week before the onset of lay and was characterized by a rapid growth of large yolky ovarian follicles and a further fall in the sensitivity of the pituitary to synthetic LH-RH. However, injections of 0·5 mg progesterone/kg resulted in a prolonged release of LH. These observations are discussed in relation to the maturation of the positive feedback mechanism by which progesterone stimulates the secretion of LH.

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DIURNAL CHANGES IN PLASMA TESTOSTERONE AND STUDIES ON PLASMA CORTICOSTEROIDS IN NON-ANAESTHETIZED MALE RHESUS MONKEYS (MACACA MULATTA)

Journal of Endocrinology ◽

10.1677/joe.0.0630325 ◽

1974 ◽

Vol 63 (2) ◽

pp. 325-335 ◽

Cited By ~ 43

Author(s):

R. P. MICHAEL ◽

K. D. R. SETCHELL ◽

T. M. PLANT

Keyword(s):

Rhesus Monkeys ◽

Plasma Testosterone ◽

Diurnal Changes ◽

Intact Male ◽

Testosterone Levels ◽

Adrenocortical Activity ◽

Peripheral Plasma ◽

Basal Plasma ◽

Competitive Protein Binding ◽

Male Rhesus

SUMMARY The assays of testosterone and corticosteroids in plasma from adult male rhesus monkeys using competitive protein-binding and radioimmunoassay techniques are described. The radioimmunoassay for testosterone was conducted without chromatography and, therefore, additionally estimated 17β-hydroxy-5α-androstan-3-one (dihydrotestosterone). Levels of testosterone in the peripheral plasma of 14 intact male rhesus monkeys showed marked fluctuations over a period of 24 h. Concentrations of testosterone at 22.00 h (1776 ± 814 ( ± s.d.) ng/100 ml) were approximately double those at 08.00 h (858 ± 407 ng/100 ml), 12.00 h (898 ± 316 ng/100 ml) and 16.00 h (784 ± 530 ng/100 ml). Castration resulted in low plasma testosterone levels (85 ± 29 ng/100 ml), and the increases at 22.00 h were no longer observed. In intact males, the 'basal' plasma corticosteroidlevel(08.00 h) was 22·4 ± 6·0 μg/100 ml. Administration of synthetic corticotrophin raised plasma corticosteroid levels without changing plasma testosterone concentration. Because plasma testosterone levels were not related to changes in adrenocortical activity, the noctural rises appear to be due to changes in testicular secretion.

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PRE-OVULATORY PROGESTERONE, THE ADRENAL CORTEX AND THE 'CRITICAL PERIOD' FOR LUTEINIZING HORMONE RELEASE IN RATS

Journal of Endocrinology ◽

10.1677/joe.0.0500029 ◽

1971 ◽

Vol 50 (1) ◽

pp. 29-39 ◽

Cited By ~ 61

Author(s):

H. H. FEDER ◽

K. BROWN-GRANT ◽

C. S. CORKER

Keyword(s):

Luteinizing Hormone ◽

Critical Period ◽

Plasma Corticosterone ◽

Release Mechanism ◽

Progesterone Concentration ◽

Corticosterone Concentration ◽

Expected Time ◽

Peripheral Plasma ◽

Dexamethasone Phosphate ◽

Lh Release

SUMMARY During the day of pro-oestrus in rats showing regular 4-day oestrous cycles, the concentration of progesterone in peripheral plasma increased slowly from 09.30 to 13.30 h and more rapidly during and after the 'critical period' for luteinizing hormone (LH) release to reach a level of 24·4 ng/ml at 21.00 h. Administration of sodium pentobarbitone at 07.00 or 13.30 h (but not at 16.30) on the day of pro-oestrus delayed ovulation and also prevented the rise in progesterone concentration at 21.00 h on that day. Levels were found to be high 24 h later on the evening of the day preceding the delayed ovulation. It is concluded that the major rise during and after the 'critical period' is the result of LH stimulation of ovarian progesterone secretion. The possibility that the gradual increase in peripheral plasma progesterone concentration that occurred before the 'critical period' was due to adrenal secretion and played some role in facilitating the onset of the ovulatory surge of LH was examined. The rise in plasma corticosterone concentration roughly paralleled that of progesterone up to the 'critical period' but the curves for the two steroids later became divergent. Suppression of adrenal activity during pro-oestrus by the administration of dexamethasone phosphate resulted in a blockade of ovulation which could be reversed by the administration of either progesterone or corticotrophin (ACTH). Conversely, blockade of ovulation followed ACTH administration at metoestrus and approximately 50% of animals adrenalectomized or sham-adrenalectomized at metoestrus or dioestrus failed to ovulate at the expected time. In adrenalectomized rats tested 12–15 days after operation, the period of pro-oestrus during which sodium pentobarbitone administration could block ovulation was more prolonged than in intact rats. The possible roles of progesterone of adrenal origin in facilitating LH release and entraining the LH release mechanism to the light—dark rhythm and of progesterone of ovarian origin in ensuring full sexual receptivity are discussed.

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

Acta Endocrinologica ◽

10.1530/acta.0.1020499 ◽

1983 ◽

Vol 102 (4) ◽

pp. 499-504 ◽

Cited By ~ 15

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.

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Role of Ca2+ and Na+ on luteinizing hormone release from the calf pituitary

AJP Endocrinology and Metabolism ◽

10.1152/ajpendo.1988.255.4.e469 ◽

1988 ◽

Vol 255 (4) ◽

pp. E469-E474

Author(s):

J. P. Kile ◽

M. S. Amoss

Keyword(s):

Luteinizing Hormone ◽

Ionophore A23187 ◽

Channel Blockers ◽

Hormone Release ◽

Primary Cells ◽

Rat Pituitary ◽

Voltage Dependent ◽

Lh Release ◽

Ca2 Channels

It has been proposed that gonadotropin-releasing hormone (GnRH) stimulates Ca2+ entry by activation of voltage-independent, receptor-mediated Ca2+ channels in the rat gonadotroph. Little work has been done on the role of calcium in GnRH-induced luteinizing hormone (LH) release in species other than the rat. Therefore, this study was done to compare the effects of agents that alter Ca2+ or Na+ entry on LH release from calf anterior pituitary primary cells in culture. GnRH (100 ng/ml), Ca2+ ionophore A23187 (2.5 microM), and the depolarizing agent ouabain (0.1-10 microM) all produced significant increases (P less than 0.05) in LH release; these effects were significantly reduced when the cells were preincubated with the organic Ca2+ channel blockers nifedipine (1-10 microM) and verapamil (1-10 microM) and with Co2+ (0.01-1 mM). The effect of ouabain was inhibited by tetrodotoxin (TTX; 1-10 nM) as well as by nifedipine at 0.1-10 microM. In contrast to its effect on rat pituitary LH release, TTX significantly inhibited GnRH-stimulated LH release at 1-100 nM. These results suggest that GnRH-induced LH release may employ Ca2+ as a second messenger in bovine gonadotrophs and support recent speculation that GnRH-induced Ca2+ mobilization may in part be voltage dependent.

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EFFECT OF HYPOTHALAMIC DEAFFERENTATION ON THE CONTROL OF LUTEINIZING HORMONE SECRETION

Journal of Endocrinology ◽

10.1677/joe.0.0460001 ◽

1970 ◽

Vol 46 (1) ◽

pp. 1-7 ◽

Cited By ~ 30

Author(s):

S. TALEISNIK ◽

M. E. VELASCO ◽

J. J. ASTRADA

Keyword(s):

Luteinizing Hormone ◽

Negative Feedback ◽

Positive Feedback ◽

Hormone Secretion ◽

Feedback Effect ◽

Luteinizing Hormone Secretion ◽

Ovarian Steroids ◽

Medial Hypothalamus ◽

Lh Release ◽

Positive Feedback Effect

SUMMARY The influence that the interruption of the neural afferents to the hypothalamus exerts on ovulation and on the release of luteinizing hormone (LH) was studied in the rat. Animals with retrochiasmatic sections interrupting the neural connexions between the medial hypothalamus and the preoptic area (POA) showed constant oestrus and failed to ovulate. Animals in which the dorsal neural afferents to the POA were transected had oestrous cycles and ovulated normally. The positive feedback effect of progesterone on LH release in spayed animals primed either with 20 μg. oestradiol benzoate or 2·5 mg. testosterone propionate 3 days before was studied. Transection of the dorsal afferents to the POA favoured an increase in plasma LH, but in animals with retrochiasmatic sections the response was abolished. However, the negative feedback effect of ovarian steroids operated after both types of transection because an increase in plasma LH occurred after ovariectomy. It is concluded that the negative feedback effect of ovarian steroids acts on the medial hypothalamus which can maintain a tonic release of gonadotrophins in the absence of steroids. In contrast, the POA involved in the positive feedback effect of progesterone is concerned with the phasic release of LH.

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