VARIATIONS IN PLASMA CONCENTRATIONS OF α-MELANOCYTE-STIMULATING HORMONE DURING THE OESTROUS CYCLE OF THE RAT AND AFTER ADMINISTRATION OF OVARIAN STEROIDS

1981 ◽  
Vol 88 (1) ◽  
pp. 73-80 ◽  
Author(s):  
A. J. THODY ◽  
C. A. WILSON ◽  
P. D. LUCAS ◽  
C. FISHER
Keyword(s):  
Single Injection ◽  
Dark Period ◽  
Plasma Concentrations ◽  
Oestrous Cycle ◽  
Ovariectomized Rats ◽  
Ovarian Steroids ◽  
Melanocyte Stimulating Hormone ◽  
Oestradiol Benzoate ◽  
Stimulating Hormone

Plasma concentrations of α-melanocyte-stimulating hormone (α-MSH) were measured by radioimmunoassay at various times during the oestrous cycle of the rat. Variations in plasma α-MSH concentrations occurred throughout the oestrous cycle. Plasma α-MSH concentrations were low during the day of dioestrus 1 and rose during the evening reaching peak levels at around 02.00 and 06.00 h on dioestrus 2. Plasma α-MSH concentrations then fell and remained low throughout the rest of dioestrus 2. A different pattern was observed during pro-oestrus and oestrus. On those days peak α-MSH concentrations occurred during the morning and persisted until the onset of the dark period at around 17.00 h. Plasma α-MSH concentrations in ovariectomized rats were found to be increased 24 h after administration of a single injection of oestradiol benzoate and at 12 and 36 h after a single injection of progesterone. It is suggested that these ovarian steroids may influence the rhythm in plasma α-MSH concentration that occurs during the oestrous cycle.

RESTORATION BY OESTRADIOL BENZOATE OF A NEURAL AND HORMONAL RHYTHM IN THE OVARIECTOMIZED RAT

1975 ◽  
Vol 64 (1) ◽  
pp. 27-35 ◽  
Author(s):  
F. R. BURNET ◽  
P. C. B. MACKINNON
Keyword(s):  
Single Injection ◽  
Time Of Day ◽  
Ovariectomized Rats ◽  
Female Rat ◽  
Functional Link ◽  
Initial Injection ◽  
Oestradiol Benzoate ◽  
Before And After ◽  
Lh Release ◽  
The Brain

SUMMARY The rate of [35S]methionine incorporation into protein in discrete cerebral areas was measured before and after the administration of oestradiol benzoate (OB) to chronically ovariectomized rats. The circadian rhythm of incorporation which is normally seen in the intact cyclic female rat was deleted by ovariectomy. A daily rhythm of incorporation reappeared, however, in all the brain areas studied 30 h after a single injection of OB (20 μg), and was still present 12 days later. The release of luteinizing hormone (LH) after administration of 20 μg OB was measured in chronically ovariectomized animals and was found to be biphasic. High levels of LH after ovariectomy were initially reduced by negative feedback, but this phase was followed 52 h later by a facilitation of LH release between 15.00 and 18.00 h. The facilitation of LH release at this time of day was still detectable 12 days after the initial injection. The evidence for a functional link between the rhythm of neural activity which is reflected by [35S]methionine incorporation, and the ability to 'time' the facilitation of LH release is discussed.

scholarly journals Plasma profiles of adrenocorticotropic hormone, cortisol, α-melanocyte-stimulating hormone, and growth hormone in dogs with pituitary-dependent hyperadrenocorticism before and after hypophysectomy

2006 ◽  
Vol 190 (3) ◽  
pp. 601-609 ◽  
Author(s):  
J M Hanson ◽  
H S Kooistra ◽  
J A Mol ◽  
E Teske ◽  
B P Meij
Keyword(s):  
Plasma Cortisol ◽  
Adrenocorticotropic Hormone ◽  
Plasma Concentrations ◽  
Pulse Frequency ◽  
Cortisol Concentration ◽  
Melanocyte Stimulating Hormone ◽  
Plasma Cortisol Concentration ◽  
Before And After ◽  
Basal Plasma ◽  
Stimulating Hormone

The 6-h plasma profiles of adrenocorticotropic hormone (ACTH), cortisol, α-melanocyte-stimulating hormone (α-MSH), and GH were studied in 17 dogs with pituitary-dependent hyperadrenocorticism (PDH) before and after hypophysectomy. The aim of the study was to investigate the relation between the hormone profile characteristics and recurrence of PDH after surgery. The hormones were secreted in a pulsatile fashion. The basal plasma cortisol concentration and area under the curve (AUC) for cortisol were significantly higher in the PDH cases than in eight controls. The characteristics of the plasma profiles of ACTH and α-MSH were not significantly different between the PDH cases and the controls. In the PDH cases, less GH was secreted in pulses than in the controls, but the difference was not significant. The basal plasma cortisol concentration, the AUC for ACTH and cortisol, and the pulse frequency of ACTH and cortisol decreased significantly after hypophysectomy for the group of PDH cases. The basal plasma concentrations of ACTH and α-MSH, the AUC for α-MSH, and the characteristics of the plasma GH profiles of the PDH cases remained unchanged after hypophysectomy. No pulses of α-MSH were observed after hypophysectomy. The co-occurrence between the ACTH and cortisol pulses decreased significantly with hypophysectomy. The postoperative pulse frequency of ACTH was the only characteristic with predictive value for the recurrence of PDH after hypophysectomy. The results of this study demonstrate that ACTH, cortisol, α-MSH, and GH are secreted in a pulsatile fashion in dogs with PDH. Hypophysectomy effectively reduces the secretion of ACTH and cortisol. The presence of ACTH pulses after hypophysectomy is a risk factor for the recurrence of hyperadrenocorticism.

RELEASE OF GONADOTROPHIN IN OVARIECTOMIZED MICE AFTER EXPOSURE TO MALES

1969 ◽  
Vol 44 (3) ◽  
pp. 293-297 ◽  
Author(s):  
F. H. BRONSON ◽  
C. DESJARDINS
Keyword(s):  
Luteinizing Hormone ◽  
Follicle Stimulating Hormone ◽  
Plasma Concentrations ◽  
Neural Pathway ◽  
Ovariectomized Mice ◽  
Oestradiol Benzoate ◽  
Stimulating Hormone

SUMMARY Gonadectomized female C57BL/6J mice were caged with males to determine the effect of male stimuli on release of follicle-stimulating hormone (FSH) and luteinizing hormone (LH). Concentrations of hypophysial and plasma FSH were significantly higher after 3 days of exposure to males when compared with controls maintained in the absence of a male. Hypophysial and plasma concentrations of LH were also higher in females caged with males, but not significantly so. Ovariectomized females were given 0·01 μg. oestradiol benzoate daily for 4 days in a second experiment and the effect of cohabitation re-evaluated. There were no significant effects of exposure to males on either FSH or LH after the oestradiol injections. Therefore the presence of males enhances synthesis and release of FSH in gonadectomized females. In addition, the results of the second experiment suggest that oestrogen interferes with this response in some way, possibly blocking the neural pathway utilized by male stimuli.

Seasonal and photoperiod-induced changes in the secretion of α-melanocyte-stimulating hormone in Soay sheep: temporal relationships with changes in β-endorphin, prolactin, follicle-stimulating hormone, activity of the gonads and growth of wool and horns

1995 ◽  
Vol 144 (3) ◽  
pp. 471-481 ◽  
Author(s):  
G A Lincoln ◽  
B I Baker
Keyword(s):  
Blood Plasma ◽  
Follicle Stimulating Hormone ◽  
Plasma Concentrations ◽  
Fold Increase ◽  
Molar Ratio ◽  
Pars Intermedia ◽  
Soay Sheep ◽  
Melanocyte Stimulating Hormone ◽  
Short Days ◽  
Stimulating Hormone

Abstract Blood plasma concentrations of α-melanocyte-stimulating hormone (α-MSH), β-endorphin (β-END), prolactin and follicle-stimulating hormone (FSH), and associated changes in the size of the testes, and growth of the horns and pelage were measured in male (n=8), castrated male (n=5) and female (n=9) Soay sheep. The animals were born in April and kept outdoors near Edinburgh (56 °N) during the first two years of life. In all groups there was a close association between the weekly changes in the plasma concentrations of α-MSH and β-END; the molar ratio in mean concentrations was close to 1:1. The blood plasma concentrations of both hormones varied markedly with season with a 3- to 10-fold increase in concentrations from the minimum in winter to the maximum in autumn. The seasonal peak occurred in September in the first year of life as juveniles, and between July (males) and September (females) in the second year when the animals were sexually mature. The plasma concentrations of ACTH did not vary in parallel with the seasonal changes in the concentrations of α-MSH (measured only in males); the molar ratio for the concentrations of α-MSH:ACTH was 1:0·12. The seasonal increase in the concentrations of α-MSH occurred 1–3 months after the seasonal increase in the concentrations of prolactin and the associated growth in horns and pelage, and slightly before, or coincident with the seasonal increase in the concentrations of FSH and the growth in the testes. In a second experiment, the same parameters were measured in a group of adult male Soay sheep (n=8) housed indoors under an artificial lighting regimen of alternating 16-week periods of long (16 h light:8 h darkness) and short days (8 h light:16 h darkness). In this situation, there was a clearly defined photoperiod-induced cycle in the plasma concentrations of α-MSH with a 25-fold increase from a minimum under long days to a maximum under short days. The concentrations of β-END varied in close parallel with the changes in α-MSH, and the temporal associations with the changes in the other pituitary hormones were similar to those observed in animals housed outdoors. Overall, the results support the view that α-MSH is co-secreted with β-END from the melanotrophs in the pars intermedia of the pituitary gland, and that the secretory activity of the melanotrophs changes markedly with season, increasing in summer and autumn, and decreasing in winter and spring. The annual cycle in daylength is likely to be the principle environmental cue timing the cycle in α-MSH and β-END. α-MSH is known to have biological effects in the brain (neuroendocrine control of prolactin and FSH), and in the adrenal gland (secretion of glucocorticoids), adipose tissue (fat storage), and skin (melanogenesis and secretion of sebum). Thus the seasonal increase in the secretion of α-MSH may regulate multiple physiological changes in autumn in preparation for winter. Journal of Endocrinology (1995) 144, 471–481

OESTRADIOL-17α AND PITUITARY RESPONSIVENESS TO LUTEINIZING HORMONE RELEASING FACTOR IN THE RAT: A STUDY USING RECTANGULAR PULSES OF OESTRADIOL-17β MONITORED BY NON-CHROMATOGRAPHIC RADIOIMMUNOASSAY

1977 ◽  
Vol 73 (3) ◽  
pp. 441-453 ◽  
Author(s):  
S. R. HENDERSON ◽  
CHRISTINE BAKER ◽  
G. FINK
Keyword(s):  
Luteinizing Hormone ◽  
Priming Effect ◽  
Plasma Concentrations ◽  
Oestrous Cycle ◽  
Facilitatory Effect ◽  
Oestradiol Benzoate ◽  
High Doses ◽  
Plasma Oestradiol

SUMMARY Plasma concentrations of oestradiol-17β were measured by a non-chromatographic radioimmunoassay during the oestrous cycle, after the s.c. injection of 2·5 or 10 pg oestradiol benzoate (OB), or the s.c. implantation of Silastic capsules containing crystalline oestradiol-17β. The profile of endogenous plasma oestradiol-17β concentrations was similar to that reported by other workers, and lay between the concentrations produced by the low and high doses of OB. The rectangular pulses of increased plasma oestradiol concentrations, produced during the period of implantation of the Silastic capsules, were used to determine the time taken for oestradiol-17β to exert its facilitatory effect on the gonadotrophin response to LH-releasing factor (RF). In animals ovariectomized at dioestrus, oestradiol, at concentrations similar to those reached during the peak of the spontaneous surge, first reduced the LH response. However, after 7 h, responsiveness increased significantly to reach a peak at 12 h. The FSH response was also greatest 12 h after ovariectomy. In animals ovariectomized at metoestrus the effect of oestradiol on the LH response was significantly less than in rats ovariectomized at dioestrus, and the FSH responses were lower than those in animals bearing empty capsules and examined at the same time after ovariectomy. These findings together with the effects of long-term exposure to sodium pentobarbitone are considered with respect to the possible mechanisms, including the priming effect of LH-RF, which may produce increased pituitary responsiveness after ovariectomy and exposure to oestrogen.

INDUCTION OF SEXUAL RECEPTIVITY BY OESTRADIOL BENZOATE IN CYCLIC FEMALE RATS: INFLUENCE OF OVARIAN SECRETIONS BEFORE INJECTION OF OESTRADIOL BENZOATE

1979 ◽  
Vol 80 (3) ◽  
pp. 389-395 ◽  
Author(s):  
P. SÖDERSTEN ◽  
S. HANSEN
Keyword(s):  
Sexual Behaviour ◽  
Oestrous Cycle ◽  
Female Rats ◽  
Ovariectomized Rats ◽  
Sexual Receptivity ◽  
Behavioural Effect ◽  
Progesterone Treatment ◽  
Oestradiol Benzoate

The ability of cyclic female rats to show sexual receptivity 24 h after an injection of 2 μg oestradiol benzoate (OB) was lost 24 h after ovariectomy. Exposure of cyclic rats to anti-oestrogen (nitromophene monocitrate) implants 24 h before ovariectomy and OB treatment prevented the latter from inducing sexual receptivity within 24 h of administration. Treatment of ovariectomized rats with constant release implants filled with an oil solution of 15 μg oestradiol/ml had no behavioural effect in itself, but prepared the rats to show lordosis 24 h after administration of OB. Progesterone treatment (4 mg) induced sexual behaviour in cyclic rats on days other than that of the oestrous cycle when the rats are normally receptive. Evidence is presented that a lower level of oestradiol stimulation than that present during pro-oestrus was needed for the induction of sexual receptivity in ovariectomized rats. It is suggested that the low basal level of oestradiol which was present throughout the oestrous cycle was necessary for the induction of sexual receptivity and that an increase in oestradiol stimulation served to increase the behavioural sensitivity to progesterone.

DEVELOPMENT OF A RADIOIMMUNOASSAY FOR α-MELANOCYTE-STIMULATING HORMONE IN THE RAT

1975 ◽  
Vol 67 (3) ◽  
pp. 385-395 ◽  
Author(s):  
A. J. THODY ◽  
R. J. PENNY ◽  
DEL CLARK ◽  
CHRISTINE TAYLOR
Keyword(s):  
Single Injection ◽  
Rat Plasma ◽  
Anterior Lobe ◽  
Adult Rats ◽  
Rat Serum ◽  
Melanocyte Stimulating Hormone ◽  
Neurointermediate Lobe ◽  
Specific Radioimmunoassay ◽  
The Mean ◽  
Stimulating Hormone

SUMMARY A sensitive and specific radioimmunoassay for α-melanocyte-stimulating hormone (α-MSH) was developed. Extracts of the neurointermediate lobe of the rat produced displacement curves which were parallel to those obtained with synthetic α-MSH. The mean immunoreactive a-MSH concentration in neurointermediate lobes from normal adult rats was 2768 ± 200 (s.e.m.) ng/lobe. This accounted for approximately 78% of the MSH activity of the neurointermediate lobe as measured by bioassay. Much lower levels of immunoreactive α-MSH were found in the anterior lobe of the rat. Extracts of rat serum and plasma also contained immunoreactive α-MSH and the mean level was found to be 237 ± 20 pg/ml. This was slightly lower than the level measured in rat plasma by bioassay. Increased levels of α-MSH were found in plasma of rats 1 and 3 h after a single injection of trifluoperazine and after 1·5 min of ether anaesthesia. These changes were reflected by decreases in the α-MSH content of the neurointermediate lobe.

Des-acetylated variants of α-melanocyte-stimulating hormone and β-endorphin can antagonize the mammotrope-recruiting activity of their acetylated forms

1993 ◽  
Vol 139 (2) ◽  
pp. 295-300 ◽  
Author(s):  
E. Ellerkmann ◽  
R. D. Kineman ◽  
T. E. Porter ◽  
L. S. Frawley
Keyword(s):  
Cell Cultures ◽  
Anterior Pituitary ◽  
Relative Number ◽  
Pituitary Cell ◽  
Ovariectomized Rats ◽  
Anterior Pituitary Cell ◽  
Melanocyte Stimulating Hormone ◽  
Absolute Requirement ◽  
Stimulating Hormone

ABSTRACT We have previously reported that hypophysial neurointermediate lobe peptides, di-acetylated α-melanocyte-stimulating hormone (di-ac-α-MSH) and N-acetylated β-endorphin (N-ac-β-END), can acutely increase the relative number of prolactin-secreting cells in anterior pituitary cell cultures from ovariectomized rats. Inasmuch as the des-acetylated forms of these peptides (des-ac-α-MSH and β-END) were not effective in this regard, we concluded that acetylation was an absolute requirement for manifestation of the recruitment response. The aim of the present study was to determine whether these des-acetylated variants could antagonize the mammotrope-recruiting activity of their acetylated congeners. Treatment of anterior pituitary cell cultures with di-ac-α-MSH and N-ac-β-END increased the relative amount of prolactin secretors above control values. Interestingly, des-acetylated variants of α-MSH and β-END blocked the mammotrope-recruitment activity of their respective acetylated forms. In addition, β-END antagonized the mammotrope-recruitment activity of di-ac-α-MSH while des-ac-α-MSH did not attenuate the stimulatory effect of N-ac-β-END. Given that mammotropes maintained in vivo are exposed to all these peptides, it is possible that these acetylated and non-acetylated congeners may act in an opposing manner to regulate dynamic prolactin release. Journal of Endocrinology (1993) 139, 295–300

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