scholarly journals Biosynthesis and degradation of prolactin in the rat anterior pituitary gland. Time course of incorporation of label in vitro and evidence for rapid degradation

1979 ◽  
Vol 182 (3) ◽  
pp. 735-743 ◽  
Author(s):  
R Shenai ◽  
M Wallis
Keyword(s):  
Anterior Pituitary ◽  
Time Course ◽  
Physiological Mechanism ◽  
Female Rats ◽  
Before And After ◽  
Apparent Decrease ◽  
Pituitary Glands ◽  
Prolactin Synthesis ◽  
Most Probable Explanation

Biosynthesis of prolactin was studied in anterior pituitary glands from female rats, incubated in vitro. In this system [3H]leucine was incorporated into pituitary proteins, including somatotropin (growth hormone) and prolactin. The rate of uptake of label into prolactin (and to a lesser extent into total protein) slowed considerably during the first 2 h of incubation, although the rate of uptake into somatotropin was constant for 8 h. The most probable explanation for this apparent decrease in the rate of prolactin synthesis is degradation of prolactin in the gland. Degradation of this hormone was also demonstrated by incubating prelabelled pituitaries in unlabelled medium and following the content of labelled prolactin, and by studying the hormonal content of pituitary glands (by radioimmunoassay) before and after incubation. Degradation of prolactin appears to be much more rapid than that of somatotropin, and may represent a physiological mechanism whereby over-accumulation of prolactin is prevented when secretion of the hormone has been rapidly switched off.

The Ultrastructural Basis For Increased Prolactin Synthesis and Release From Anterior Pituitary Glands of Estrogen-Progesterone Primed Ovariectomized Rats: Correlated Electron Microscopy and Radioimmunoassay

1973 ◽  
Vol 31 ◽  
pp. 564-565
Author(s):  
P. W. Coates ◽  
C. A. Blake ◽  
D. S. Maxwell ◽  
C. H. Sawyer
Keyword(s):  
Anterior Pituitary ◽  
Elevated Serum ◽  
Virgin Female ◽  
Estradiol Benzoate ◽  
Female Rats ◽  
Ovariectomized Rats ◽  
Serum Prolactin ◽  
Electron Microscopic ◽  
Pituitary Glands ◽  
Prolactin Synthesis

In rats, physiological studies show that ovariectomy results in a reduced concentration of circulating prolactin. Conversely, ovariectomized rats given estrogen have elevated serum prolactin and increased amounts of prolactin in the anterior pituitary gland. Separate electron microscopic studies suggest modifications in fine structure of prolactin producing (LTH) cells based on relatively large cumulative amounts of estrogen given alone or with comparably high doses of progesterone to adult virgin female or ovariectomized rats. This study was undertaken to provide a correlated morphological and physiological investigation of LTH cells and prolactin levels in a model commonly used by many researchers.Six to seven weeks after bilateral ovariectomy, a group of adult female rats was primed by a subcutaneous injection of 50 ng of estradiol benzoate and 25 mg of progesterone.

Effects of two enkephalin analogues, morphine sulphate, dopamine and naloxone on prolactin secretion from rat anterior pituitary glands in vitro

1986 ◽  
Vol 109 (3) ◽  
pp. 313-320 ◽  
Author(s):  
A. M. Bentley ◽  
M. Wallis
Keyword(s):  
Anterior Pituitary ◽  
Time Course ◽  
Opiate Receptors ◽  
Inhibitory Effect ◽  
Antagonistic Effect ◽  
Prolactin Secretion ◽  
Morphine Sulphate ◽  
Low Concentrations ◽  
Pituitary Glands

ABSTRACT Experiments were carried out on the antagonistic effects of opiates on the inhibition by dopamine of prolactin secretion from rat anterior pituitary glands. Dose–response and time-course experiments were carried out using both static incubation of paired hemipituitary glands and perifusion of whole glands. Dopamine (10–1000 nmol/l) was found to have an inhibitory effect on prolactin secretion, but at a lower concentration (0·1 nmol/l) a small stimulation was observed. Against an inhibition established with 100 nmol dopamine/l in static incubation, the three opiates under study, morphine sulphate, Leu5enkephalin and d-Ala2,Met5-enkephalin (DAME), had a maximum antagonistic effect at 50–1000 nmol/l in a 90-min incubation. Morphine and DAME were rather more effective than Leu5-enkephalin, possibly because of degradation of the latter. Naloxone reversed the effect of morphine. All three opiates showed little effect on dopamine-inhibited prolactin secretion in a perifusion system. The data accord with previous suggestions that prolactin secretion may be stimulated both by very low concentrations of dopamine and by opiates acting to reverse the inhibition exerted by higher dopamine concentrations. It should be noted that both morphine and the enkephalins have similar effects on prolactin secretion, despite their normal specificity for different opiate receptors; their actions on the pituitary may thus be rather non-specific. J. Endocr. (1986) 109, 313–320

2-Hydroxyoestradiol acutely inhibits prolactin secretion from the superfused pituitary glands of normal female rats: evidence for a cyclical effect

1986 ◽  
Vol 111 (2) ◽  
pp. 199-204 ◽  
Author(s):  
P. K. Banks ◽  
S. E. Inkster ◽  
N. White ◽  
S. L. Jeffcoate
Keyword(s):  
Suppressive Effect ◽  
Prolactin Secretion ◽  
Female Rats ◽  
Normal Female ◽  
Female Rat ◽  
Naturally Occurring ◽  
Before And After ◽  
Pituitary Glands ◽  
Layer Chromatography

ABSTRACT Catecholoestrogens are naturally occurring metabolites of oestrogens which are found in brain tissue and for which a neuroendocrine role has been postulated. However, reports of their effects on prolactin secretion are ambiguous and as yet no defined function has been attributed to them. The effects of 2-hydroxyoestradiol (2-OHE2) and dopamine on the release of prolactin in vitro by perfused pituitary glands from normal adult female rats at different stages of the oestrous cycle have been investigated. The purity and stability of the 2-OHE2 preparation before and after exposure to pituitary tissue was confirmed by radioenzymatic assay and subsequent thin-layer chromatography. Dopamine (500 nmol/l, 100 nmol/l) was found consistently to suppress release by 60%; this effect was immediate and reversible upon removal of the dopamine. In contrast, the effects of 2-OHE2 (10 nmol/l, 100 nmol/l) were found to vary during the cycle. No effect on prolactin release was evident during either dioestrus or pro-oestrus, but during oestrus a similar, though less potent, suppression of prolactin secretion to that of dopamine was observed (35% suppression compared with controls). The cyclical variation in the suppressive effect of 2-OHE2 on prolactin secretion in the female rat is compatible with a postulated neuroendocrine role for this catecholoestrogen. J. Endocr. (1986) 111, 199–204

Time course of inhibition of synthesis and basal release of FSH from pituitary glands of female rats by bovine follicular fluid in vitro

1982 ◽  
Vol 101 (4) ◽  
pp. 501-506 ◽  
Author(s):  
A. A. J. Jenner ◽  
J. de Koning ◽  
G. P. van Rees
Keyword(s):  
Follicular Fluid ◽  
Time Course ◽  
Mechanisms Of Action ◽  
Female Rats ◽  
Ovariectomized Rats ◽  
Intact Female ◽  
In Vitro Technique ◽  
Basal Release ◽  
Pituitary Glands

Abstract. Inhibin-like activity in steroid-free bovine follicular fluid (bFF) is demonstrated using an in vitro technique with hemi-pituitary glands from intact female (second day of dioestrus) and ovariectomized rats: synthesis as well as basal release of FSH, but not of LH, are inhibited profoundly. The results confirm and extend data from other investigators on the action of inhibin-like material. The effect of the inhibin-like activity is shown to be reversible, as synthesis and the rise of basal release are restored when bFF is withdrawn from the incubation medium. Synthesis of FSH seems to be inhibited earlier than basal release, and it is suggested that the inhibin-like material acts only directly on FSH synthesis. Some possibilities of the mechanisms of action of inhibin-like activity are discussed.

scholarly journals In vitro effect of leptin on LH release by anterior pituitary glands from female rats at the time of spontaneous and steroid-induced LH surge

2001 ◽  
pp. 659-665 ◽  
Author(s):  
SN De Biasi ◽  
LI Apfelbaum ◽  
ME Apfelbaum
Keyword(s):  
Estrous Cycle ◽  
Anterior Pituitary ◽  
Female Rats ◽  
Female Rat ◽  
Lh Surge ◽  
Pituitary Glands ◽  
Lh Release ◽  
Vitro Effect ◽  
Stimulation Of

OBJECTIVE: The purpose of this work was to study the direct effect of leptin on LH release by anterior pituitary glands from female rats at the time of spontaneous and steroid-induced LH surge. METHODS: LH responsiveness to leptin by pituitaries from rats killed in the afternoon (1500 h) at different stages of the 4-day estrous cycle (diestrus-1: D1; diestrus-2: D2; proestrus; estrus), ovariectomized (OVX; 15 days post-castration) and ovariectomized steroid-primed (OVX-E(2)/Pg; pretreated with 5 microg estradiol and 1 mg progesterone), was evaluated in vitro. Hemi-adenohypophyses were incubated in the presence of synthetic murine leptin for 3 h. RESULTS: Addition of increasing concentrations of leptin (0.1-100 nmol/l) to the incubation medium of proestrus pituitaries produced a dose-related stimulation of LH release; the maximal increase to 315% of control was obtained with 10 nmol/l leptin. Leptin (10 nmol/l) enhanced LH release at all days of the estrous cycle, the greatest response occurring in proestrus (318%) and the lowest at D1 (123%). In order to evaluate the role of nitric oxide (NO) in the action of leptin on LH release, glands from proestrus rats were incubated in the presence of 10 nmol/l leptin with or without 0.3 mmol/l N(G)-monomethyl-l-arginine (NMMA), a competitive inhibitor of NO synthase (NOS). NMMA completely suppressed the stimulation of LH release induced by leptin. Leptin also stimulated LH release by pituitaries from OVX rats, and treatment with steroid hormones led to a marked increase in the response (OVX: 162% compared with OVX-E(2)/Pg: 263%; P<0.05). For comparative analysis, a similar experimental procedure was carried out using GnRH (10 nmol/l). Leptin acts at the pituitary level in a similar manner as GnRH, although with significantly lower potency. CONCLUSIONS: These results confirm and extend previous reports regarding a direct action of leptin at the pituitary level, stimulating LH release by anterior pituitaries from female rats at the time of spontaneous and steroid-induced LH surge. In the female rat pituitary this leptin action is controlled by gonadal steroids and mediated by NO.

Size heterogeneity of prolactin secreted from and stored in the rat anterior pituitary gland in vitro

1984 ◽  
Vol 4 (2) ◽  
pp. 129-137 ◽  
Author(s):  
Andrew M. Bentley ◽  
Teresa K. Surowy ◽  
Michael Wallis
Keyword(s):  
Anterior Pituitary ◽  
Relative Proportion ◽  
Gel Filtration ◽  
Prolactin Secretion ◽  
Female Rats ◽  
Pituitary Glands ◽  
Dimeric Form ◽  
Size Heterogeneity ◽  
Pituitary Prolactin

The size heterogeneity of rat pituitary prolactin was investigated using anterior pituitary glands from female rats incubated in vitro and gel filtration on Sephadex G-100. Monomeric prolactin was preferentially secreted compared with dimeric and ‘trimeric” material. When glands were incubated with dopamine, prolactin secretion was inhibited and the relative proportion of dimer in the gland (but not the medium) was decreased. Morphine sulphate reversed the effect of dopamine on prolactin secretion and on the proportion of prolactin in the gland that was in the dimeric form. The results suggest that monomeric prolactin is more readily secreted than dimer, and that dopamine decreases the production or stability of the dimer.

Autonomous FSH synthesis in vitro in anterior pituitary glands and grafts from female rats

1991 ◽  
Vol 129 (1) ◽  
pp. 27-33 ◽  
Author(s):  
J. A. M. J. van Dieten ◽  
J. de Koning ◽  
G. P. van Rees
Keyword(s):  
Follicular Fluid ◽  
Anterior Pituitary ◽  
Female Rats ◽  
Regulatory Mechanisms ◽  
Ovariectomized Rats ◽  
Intact Female ◽  
Pituitary Glands

ABSTRACT When pituitary glands from intact female, but not from ovariectomized rats, are incubated for 8 h in medium TC199 without further additives, FSH is synthesized. This LHRH-independent (or autonomous) FSH synthesis is prevented when bovine follicular fluid (bFF) is added to the incubation medium. Results from preliminary experiments, however, indicate no clear autonomous FSH synthesis after long-term absence of LHRH. To investigate the regulatory mechanisms involved in autonomous FSH synthesis and release, pituitary glands (exposed to endogenous LHRH) and pituitary grafts (not exposed to endogenous LHRH) from intact and ovariectomized rats were incubated for 8 h in medium TC199. Total FSH content (FSH released plus FSH remaining in the tissue) was compared with that in non-incubated glands or grafts, giving an indication of FSH synthesis. In addition, some of the animals were given LHRH pulses for 40 h before incubation. When pituitary tissue was taken from intact female rats, FSH synthesis occurred in the animals' own glands and in grafts from LHRH-pretreated rats. No FSH synthesis was seen in ovariectomized rats with or without pretreatment with bFF and/or LHRH. However, when ovariectomized rats had been pretreated with oestrogen, FSH synthesis was measured in vitro after pulsatile LHRH treatment in vivo. The results indicate that autonomous FSH synthesis in vitro is dependent upon previous (in vivo) exposure of the glands to both oestrogen and LHRH. Journal of Endocrinology (1991) 129, 27–33

Monosodium l-glutamate administration: effects on gonadotrophin secretion, gonadotrophs and mammotrophs in prepubertal female rats

1985 ◽  
Vol 104 (2) ◽  
pp. 185-NP ◽  
Author(s):  
M. O. Dada ◽  
C. A. Blake
Keyword(s):  
Adult Female ◽  
Anterior Pituitary ◽  
Monosodium Glutamate ◽  
Volume Density ◽  
Reciprocal Relationship ◽  
Female Rats ◽  
Prolactin Cells ◽  
Gonadotrophin Secretion ◽  
Pituitary Glands

ABSTRACT We have studied gonadotrophin secretion and immunocytochemically stained gonadotrophs and mammotrophs in 35-day-old female rats which had been treated with monosodium glutamate (MSG) as neonates. We also compared our morphometric data in the saline-treated controls with those we have previously obtained in normal adult female rats. The size of the anterior pituitary glands was reduced but the serum levels, the pituitary gland concentrations and contents, and the in-vitro basal release rates of LH and FSH were not significantly altered by MSG treatment. The size of the LH and FSH cells was reduced by MSG administration, but the volume and numerical densities of LH and FSH cells, and the percentage of LH and FSH cells in the pars distalis were not affected. The results suggest that in spite of the smaller size of LH and FSH cells and of the anterior pituitary glands in the MSG-treated rats, the cells contain normal amounts of hormone and the basal LH and FSH secretion rates of the glands are not significantly depressed, contributing to the maintenance of normal serum gonadotrophin concentrations. The volume density of prolactin cells was not increased by MSG treatment. The volume density of gonadotrophs and the percentage of cells which are gonadotrophs in anterior pituitary glands of prepubertal female rats were greater than those in adult female rats, but the reverse was true for the volume density of prolactin cells, suggesting a reciprocal relationship between the relative numbers of gonadotrophs and mammotrophs in prepubertal and adult female rats. J. Endocr. (1985) 104, 185–192

scholarly journals Biosynthesis of growth hormone in the rat anterior pituitary gland. Stimulation of biosynthesis in vitro by insulin

1973 ◽  
Vol 134 (4) ◽  
pp. 1103-1113 ◽  
Author(s):  
A. Betteridge ◽  
M. Wallis
Keyword(s):  
Growth Hormone ◽  
Anterior Pituitary ◽  
Rna Synthesis ◽  
Glucose Utilization ◽  
Actinomycin D ◽  
Hormone Synthesis ◽  
Pituitary Glands ◽  
Hormone Biosynthesis ◽  
Stimulation Of

The effect of insulin on the incorporation of radioactive leucine into growth hormone was investigated by using rat anterior pituitary glands incubated in vitro. A 50% stimulation over control values was observed at insulin concentrations above 2μm (280munits/ml). The effect was specific for growth hormone biosynthesis, over the range 1–5μm-insulin (140–700munits/ml). Lower more physiological concentrations had no significant effect in this system. Above 10μm (1.4 units/ml) total protein synthesis was also increased. The stimulation of growth hormone synthesis could be partially blocked by the addition of actinomycin D, suggesting that RNA synthesis was involved. Insulin was found to stimulate the rate of glucose utilization in a similar way to growth hormone synthesis. 2-Deoxyglucose and phloridzin, which both prevented insulin from stimulating glucose utilization, also prevented the effect of insulin on growth hormone synthesis. If glucose was replaced by fructose in the medium, the effect of insulin on growth hormone synthesis was decreased. We conclude that the rate of utilization of glucose may be an important step in mediating the effect of insulin on growth hormone synthesis.

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