scholarly journals Effects of Growth Hormone Secretagogues on Prolactin Release in Anesthetized Dwarf (dw/dw) Rats*

Endocrinology ◽  
1998 ◽  
Vol 139 (8) ◽  
pp. 3590-3596 ◽  
Author(s):  
Danielle F. Carmignac ◽  
Pamela A. Bennett ◽  
Iain C. A. F. Robinson
Keyword(s):  
Growth Hormone ◽  
Receptor Expression ◽  
Female Rats ◽  
Normal Male ◽  
Growth Hormone Secretagogues ◽  
Prolactin Release ◽  
Male And Female ◽  
Gh Secretagogues ◽  
Male And Female Rats ◽  
Tsh Levels

Abstract In addition to stimulating GH release, GH secretagogues such as GH-releasing peptide-6 (GHRP-6) stimulate small amounts of ACTH and PRL release. Although the effects on ACTH have recently been studied, there is little information about the effects of GHRP-6 on PRL. We have now studied GHRP-6-induced GH and PRL release and their regulation by estrogen (E2) in anesthetized male and female rats and in GH-deficient dwarf (dw/dw) rats that maintain high pituitary PRL stores and show elevated hypothalamic GH secretagogue receptor expression. Whereas GHRP-6 (0.1–2.5 μg, iv) did not induce PRL release in normal male or female rats, significant PRL responses were observed in dw/dw females. These responses were abolished by ovariectomy and could be strongly induced in male dw/dw rats by E2 treatment. These effects could be dissociated from GHRP-6-induced GH release in the same animals, but not from PRL release induced by TRH, which was also abolished by ovariectomy and induced in males by E2 treatment. However, the effects of GHRP-6 on PRL were unlikely to be mediated by TRH because in the same animals, TSH levels were unaffected by GHRP-6 whereas they were increased by TRH. The increased PRL response could reflect an increase in GH secretagogue receptor expression that was observed in the arcuate and ventromedial nuclei of E2-treated rats. Our results suggest that the minimal PRL-releasing activity of GHRP-6 in normal rats becomes prominent in GH-deficient female dw/dw rats and is probably exerted directly at the pituitary; these GHRP-6 actions may be modulated by E2 at both hypothalamic and pituitary sites.

Growth hormone responses to multiple injections of a fragment of human growth hormone-releasing factor in conscious male and female rats

1985 ◽  
Vol 106 (3) ◽  
pp. 281-289 ◽  
Author(s):  
R. G. Clark ◽  
I. C. A. F. Robinson
Keyword(s):  
Growth Hormone ◽  
Human Growth ◽  
Female Rats ◽  
Male Rats ◽  
Normal Male ◽  
Male And Female ◽  
Gh Secretion ◽  
Male And Female Rats ◽  
Hormone Responses ◽  
Males And Females

ABSTRACT The GH responses to single i.v. injections of GH-releasing factor (GRF) in conscious male rats are highly variable. Although normal male rats show a pulsatile secretory pattern of GH with pulses occurring at intervals of 3–3·5 h, the peaks occur at different times in individual animals. We have compared the GH responses of young conscious male and female rats to multiple i.v. injections of 1 μg human (h) GRF1-29NH2. The peak GH responses occurred 3–5 min after hGRF1-29NH2 injection and were lower in female than in male rats. Both males and females responded uniformly to hGRF1-29NH2 injections given 180 min apart and the GH responses became entrained with no endogenous GH pulsing. Female rats produced consistent GH peaks in response to hGRF1-29NH2 injections at 90-min intervals, whereas male rats responded only to alternate injections, so that GH peaks occurred only every 180 min despite giving GRF every 90 min. When the frequency of hGRF1-29NH2 administration was increased to once every 40 min female rats again responded consistently to each injection. Male rats responded intermittently, being able to respond to two injections 40 min apart, after which they became refractory to hGRF1-29NH2. This cycle of varying sensitivity to GRF in male rats probably underlies their 3-hourly endogenous GH secretory rhythm. Female rats can respond uniformly to repeated GRF injections, consistent with their more continuous pattern of endogenous GH secretion. Introducing a pulse of 10 μg rat GH into a series of hGRF1-29NH2 injections did not induce refractoriness to hGRF1-29NH2, suggesting that GH does not itself desensitize the pituitary to GRF. Whether the different patterns of GH secretion in males and females result from different patterns of GRF and/or somatostatin secretion remains to be determined. J. Endocr. (1985) 106, 281–289

PITUITARY HORMONE SECRETION IN THE GENETICALLY MALE RAT PSEUDOHERMAPHRODITE

1975 ◽  
Vol 64 (2) ◽  
pp. 249-255 ◽  
Author(s):  
A. S. GOLDMAN ◽  
A. W. ROOT ◽  
G. DUCKETT ◽  
B. H. SHAPIRO
Keyword(s):  
Growth Hormone ◽  
Follicle Stimulating Hormone ◽  
Hormone Secretion ◽  
Female Rats ◽  
Male Rat ◽  
Normal Male ◽  
Pituitary Hormone ◽  
Male And Female ◽  
Male And Female Rats ◽  
Serum Lh

SUMMARY Pituitary content or concentration of follicle-stimulating hormone (FSH), prolactin and growth hormone in the genetically androgen insensitive male rat pseudohermaphrodite is intermediate between normal male and female rats, while pituitary luteinizing hormone (LH) concentration and serum FSH levels are the same as in the normal male. The concentration of serum LH, prolactin and growth hormone indicates no sexual dimorphism. Although the pseudohermaphrodite is genetically male with a female phenotype, our results suggest some degree of masculinization of the hypothalamicpituitary system.

INDUCTION OF GOITRE BY PTU OR KClO4 IN MALE AND FEMALE RATS. EFFECT OF GONADECTOMY

1973 ◽  
Vol 74 (1) ◽  
pp. 88-104 ◽  
Author(s):  
T. Jolín ◽  
M. J. Tarin ◽  
M. D. Garcia
Keyword(s):  
Iodine Content ◽  
High Plasma ◽  
Disc Electrophoresis ◽  
Female Rats ◽  
Male Rats ◽  
Adult Rats ◽  
Male And Female ◽  
Glucose Levels ◽  
Male And Female Rats ◽  
Tsh Levels

ABSTRACT Male and female rats of varying ages were placad on a low iodine diet (LID) plus KClO4 or 6-propyl-2-thiouracil (PTU) or on the same diet supplemented with I (control rats). Goitrogenesis was also induced with LID plus PTU in gonadectomized animals of both sexes. The weight of the control and goitrogen treated animals, and the weight and iodine content of their thyroids were determined, as well as the plasma PBI, TSH, insulin and glucose levels. The pituitary GH-like protein content was assessed by disc electrophoresis on polyacrylamide gels. If goitrogenesis was induced in young rats of both sexes starting with rats of the same age, body weight (B.W.) and pituitary growth hormone (GH) content, it was found that both the males and females developed goitres of the same size. On the contrary, when goitrogenesis was induced in adult animals, it was found that male rats, that had larger B.W. and pituitary GH content than age-paired females, developed larger goitres. However, both male and female rats were in a hypothyroid condition of comparable degree as judged by the thyroidal iodine content and the plasma PBI and TSH levels. When all the data on the PTU or KClO4-treated male and female rats of varying age and B.W. were considered together, it was observed that the weights of the thyroids increased proportionally to B.W. However, a difference in the slope of the regression of the thyroid weight over B.W. was found between male and female rats, due to the fact that adult male rats develop larger goitres than female animals. In addition, in the male rats treated with PTU, gonadectomy decreased the B.W., pituitary content of GH-like protein and, concomitantly, the size of the goitre decreased; an opposite effect was induced by ovariectomy on the female animals. However, when goitrogenesis was induced in weight-paired adult rats of both sexes, the male animals still developed larger goitres than the females. Among all the parameters studied here, the only ones which appeared to bear a consistent relationship with the size of the goitres in rats of different sexes, treated with a given goitrogen, were the rate of body growth and the amount of a pituitary GH-like protein found before the onset of the goitrogen treatment. Moreover, though the pituitary content of the GH-like protein decreased as a consequence of goitrogen treatment, it was still somewhat higher in male that in female animals. The present results suggest that GH may somehow be involved in the mechanism by which male and female rats on goitrogens develop goitres of different sizes, despite equally high plasma TSH levels.

Significance of the Secretory Pattern of Growth Hormone

Physiology ◽  
1986 ◽  
Vol 1 (2) ◽  
pp. 44-47
Author(s):  
OGP Isakkson ◽  
J-O Jansson ◽  
RG Clark ◽  
I Robinson
Keyword(s):  
Growth Hormone ◽  
Plasma Concentration ◽  
High Amplitude ◽  
Female Rats ◽  
Healthy Children ◽  
Male And Female ◽  
Male And Female Rats ◽  
Low Concentrations ◽  
Lower Amplitude ◽  
Secretory Pattern

The plasma concentration of growth hormone fluctuates widely with pronounced peaks at intervals of a few hours and troughs of nearly vanishingly low concentrations in between. The pattern of secretion varies, and different patterns affect growth differently. Tall children usually have frequent growth hormone peaks of a high amplitude, whereas short, healthy children usually have fewer peaks of a lower amplitude. Male and female rats have different patterns, and a "masculine" pattern promotes growth more than a "feminine" pattern. If the same amount of growth hormone is administered in several pulses rather than continuously, the effect on growth is much greater.

DIURNAL VARIATIONS OF PLASMA AND PITUITARY THYROTROPHIN IN ADULT MALE AND FEMALE RATS

1976 ◽  
Vol 83 (4) ◽  
pp. 745-751 ◽  
Author(s):  
Trinidad Jolín ◽  
Luis F. Pallardo ◽  
Isabel Pericás
Keyword(s):  
Circadian Rhythm ◽  
Diurnal Variations ◽  
Female Rats ◽  
Male Rats ◽  
Male And Female ◽  
Male And Female Rats ◽  
Highly Sensitive ◽  
Two Peaks ◽  
Afternoon Peak ◽  
Tsh Levels

ABSTRACT Male and female rats fed a low iodine diet for 20 days were used to study the diurnal variations in resting levels of plasma and pituitary TSH concentration using a highly sensitive radioimmunoassay. Sex differences in the fluctuations in plasma TSH levels and in amount of TSH in the pituitary gland were observed. The daily fluctuations of plasma TSH were characterized by two peaks that occurred in males at 6 a. m. and at 3 p. m., while in females the peaks were delayed until 9 a. m. and 7:30 p. m. Moreover, in the females the morning and the afternoon peaks were of the same intensity while in the males the afternoon peak that occurred just before the onset of darkness was much greater than the morning peak. There was a fall in TSH content of the pituitary in the male rats at 6 a. m. and also in the afternoon just before the onset of darkness. Thus, the diurnal variations in the plasma and pituitary TSH levels were related in male rats. In the females, however, the pituitary TSH concentration did not reflect the changes observed in the plasma TSH levels. The level of plasma PBI did not appear to be responsible for the fluctuations in plasma TSH concentration. It is suggested that the main mechanism for the control of the circadian rhythm of TSH might be related to a high activity at night.

PREVENTION OF CENTRAL DEFEMINIZATION BUT NOT MASCULINIZATION IN MALE RATS BY INHIBITION NEONATALLY OF OESTROGEN BIOSYNTHESIS

1977 ◽  
Vol 74 (3) ◽  
pp. 375-382 ◽  
Author(s):  
J. T. M. VREEBURG ◽  
PAULA D. M. VAN DER VAART ◽  
P. VAN DER SCHOOT
Keyword(s):  
Sexual Function ◽  
Ovarian Function ◽  
Testosterone Propionate ◽  
Neonatal Period ◽  
Female Rats ◽  
Male Rats ◽  
Normal Male ◽  
Male And Female ◽  
Male And Female Rats ◽  
Copulatory Behaviour

SUMMARY An inhibitor of aromatization, androsta-1,4,6-triene-3,17-dione (ATD), was administered to newborn male and female rats and various parameters of gonadal and sexual function were examined in adulthood. Males injected with 1 mg ATD on the day of birth (day 1) and on days 3, 5, 10 and 15 postnatally, subsequently (day 55) showed normal male and female copulatory behaviour, but were not able to maintain cyclicity in ovarian transplants. When the ATD was administered by Silastic implants, however, cyclicity in ovarian transplants did occur. Neither form of treatment brought about significant changes in neonatal plasma or testicular testosterone concentrations. Female rats implanted on day 3 of life with Silastic capsules containing ATD and then given an injection of 0·25 mg testosterone propionate on day 5 subsequently showed normal ovarian function, whereas the controls receiving only testosterone propionate showed persistent vaginal cornification, anovulation and polyfollicular ovaries. The results support the view that the central conversion of testicular androgens to oestrogens during the neonatal period is necessary to abolish cyclic gonadotrophin release and to suppress female copulatory behaviour.

Effects of neonatal administration of monosodium glutamate on plasma growth hormone (GH) response to GH-releasing factor in adult male and female rats

1986 ◽  
Vol 372 (2) ◽  
pp. 361-365 ◽  
Author(s):  
Ichiji Wakabayashi ◽  
Hisaaki Hatano ◽  
Shiro Minami ◽  
Yoji Tonegawa ◽  
Shigeo Akira ◽  
...  
Keyword(s):  
Growth Hormone ◽  
Adult Male ◽  
Monosodium Glutamate ◽  
Female Rats ◽  
Plasma Growth Hormone ◽  
Male And Female ◽  
Male And Female Rats ◽  
Neonatal Administration

LIVER GLUCURONIDASE ACTIVITY OF RATS IN VARIOUS EXPERIMENTAL STATES

1953 ◽  
Vol 31 (1) ◽  
pp. 18-40 ◽  
Author(s):  
Jules Tuba
Keyword(s):  
Virgin Female ◽  
Female Rats ◽  
Male Rats ◽  
Normal Male ◽  
Significant Elevation ◽  
Castrate Male ◽  
Male And Female ◽  
Glucuronidase Activity ◽  
Male And Female Rats ◽  
Hormonal Imbalance

Liver glucuronidase activity was studied in male and female rats with regard to the effect of a number of experimental factors. Virgin female and breeder female rats had significantly higher levels of the liver enzyme than males. Breeding and lactation stimulated production of liver glucuronidase and activity fell towards male values in females which had passed the breeding age. Castration of males or females had no significant effect on the enzyme. A highly significant elevation of liver glucuronidase resulted from injection of oestradiol dipropionate into castrate male rats, while testosterone dipropionate had no effect. Neither hormone affected activity of the enzyme when injected into normal male or female rats. Levels of liver glucuronidase in diabetic male rats were elevated about 50% above normal, and these statistically significant increases are assumed to be related to some hormonal imbalance

Myocardial capillaries in rats with cobalt-induced polycythemia

1959 ◽  
Vol 197 (5) ◽  
pp. 981-983 ◽  
Author(s):  
E. Lovell Becker
Keyword(s):  
Female Rats ◽  
Normal Male ◽  
Male And Female ◽  
Blood Hemoglobin ◽  
Male And Female Rats ◽  
Tissue Area

Studies have been carried out on normal male and female rats of the Carworth-Nelson strain to ascertain myocardial capillary change after cobalt-induced polycythemia. There was a significant increase in blood hemoglobin and hematocrit, but there was no significant increase in the number of myocardial capillaries. There was a statistically significant increase in the ratio of capillary to tissue area. These results secondary to polycythemia were interpreted as suggesting engorgement of capillaries or dilatation of capillaries not readily visible in control animals.

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