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.

Cell-density dependence of the rate of prolactin secretion from perifused rat anterior pituitary cells

1983 ◽  
Vol 97 (2) ◽  
pp. 221-228 ◽  
Author(s):  
A. M. Bentley ◽  
M. Wallis
Keyword(s):  
Density Dependence ◽  
Cell Density ◽  
Anterior Pituitary ◽  
Prolactin Secretion ◽  
Female Rats ◽  
Pituitary Cells ◽  
The Third ◽  
Pituitary Glands ◽  
Prolactin Content ◽  
Perifusion System

Anterior pituitary glands from female rats were dispersed enzymically in the absence of dopamine. Dispersed cells (106–107) were layered onto columns containing Bio-Gel P-2 and were then perifused for 3 h with Dulbecco's Modified Eagle's Medium. The prolactin content of the perifusate and cell homogenates was determined by radioimmunoassay. Prolactin secretion during the third hour of perifusion increased as the loading of cells increased. However, the increase was not linear, and when secretion rate per 106 cells was calculated it was found that increased loading decreased the rate, which fell to a plateau of 1·3 ± 0·1 (s.e.m.) ng/min per 106 cells at a loading of about 8 × 106 cells from 3·8 ± 0·1 ng/min per 106 cells for a loading of 106 cells. This cell-density dependence of the rate of prolactin secretion in the perifusion system may be due to intercellular contact since the isolation of the tissue removes the influence of hypothalamic factors, while localized build up of prolactin (potentially causing direct autoregulation on the lactotroph) seems unlikely because of the continuous flow of medium.

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

Isolation and Partial Characterization of Adipotropin, an Apparent New Lipolytic Peptide from Bovine Anterior Pituitary Lobes

1980 ◽  
Vol 35 (9) ◽  
pp. 1171-1177 ◽  
Author(s):  
Karen O’Malley ◽  
Karl Folkers ◽  
Olav Trygstad ◽  
Irene Foss
Keyword(s):  
Anterior Pituitary ◽  
Gel Filtration ◽  
Exchange Chromatography ◽  
Cation Exchange Chromatography ◽  
Frozen Tissue ◽  
Pituitary Glands ◽  
Approximate Molecular Weight ◽  
One Year

A peptide, apparently new, has been isolated from the anterior lobes of bovine pituitary glands by the following steps: (1) lyophilization of frozen tissue; (2) homogenization; (3) extraction with an aqueous buffer; (4) gel filtration; (5) anion and then (6) cation exchange chromatography; (7) HPLC. One antioxidant and two proteolytic inhibitors were present during buffer extraction to avoid artifactual reactions. Amino acid analyses consistently revealed the same amino acids and no others on different specimens, one year apart. The composition was estimated as: 4 Asp, 2 Thr, 5 Ser, 8 Glu(x), 5 Pro, 10 Gly, 4 Ala, 2 Val, 2 Met, 1 Ile, 2 Leu, 1 Tyr, 1 Phe, 2 His, 3 Lys, 2 Arg (5600 daltons). Cysteine and tryptophan were absent. An approximate molecular weight by gel filtration was 7200 daltons. The isoelectric point was 6.1. The peptide showed a dose-response activity in the range of 0.001-1.0 μg in a rabbit adipose system, in vitro. The peptide is tentatively designated as adipotropin, because it has no unequivocal chemical relation­ship to other relevant lipolytic peptides, and because it has the highest molar potency, in vitro, of these peptides, including pACTH.

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.

Ritonavir and Saquinavir Directly Stimulate Anterior Pituitary Prolactin Secretion, in Vitro

2002 ◽  
Vol 15 (1) ◽  
pp. 65-68 ◽  
Author(s):  
G. Orlando ◽  
L. Brunetti ◽  
M. Vacca
Keyword(s):  
Protease Inhibitors ◽  
Anterior Pituitary ◽  
Dopamine Release ◽  
Prolactin Secretion ◽  
Hiv Protease ◽  
Type I ◽  
Endogenous Dopamine ◽  
Pituitary Prolactin ◽  
Hiv 1

An association between human immunodeficiency virus type I (HIV-1) protease inhibitors (Pis) and galactorrhoea/hyperprolactinemia adverse effect has recently been reported in four HIV-1-infected women treated with Pis (indinavir, nelfinavir, ritonavir or saquinavir). This could be explained by a direct effect of ritonavir and saquinavir on anterior pituitary prolactin (PRL) release, and/or an indirect effect of Pis on the secretion of hypothalamic dopamine, which is the main PRL inhibitory factor. Anterior pituitaries were explanted from adult male Wistar rats, the cells were trypsin dispersed, plated into multiwell cultures and incubated for 1 h with either ritonavir or saquinavir (0.01 nM-1mM). PRL release into the incubation medium was evaluated by radioimmunoassay. Hypothalamic neuronal endings (synaptosomes) were prepared by tissue homogenization, incubated with [3H]dopamine, substituting for the endogenous dopamine pool, and perfused with ritonavir or saquinavir, both basally and during depolarization (K+ 15 mM)-induced dopamine release. Beta-emission from 2 min perfusate fractions, corresponding to [3H]dopamine release, was detected by liquid scintillation scanning. We found that both ritonavir and saquinavir are able to significantly stimulate PRL secretion, with saquinavir slightly more effective than ritonavir. On the contrary, both protease inhibitors do not modify either basal or depolarization-induced dopamine release. We can speculate that HIV Pis despite a high affinity for the catalytic site of HIV protease, could also bind to and inhibit homologous mammalian proteins in the anterior pituitary that are involved in PRL secretion.

Inhibition by testosterone of prolactin and growth hormone release from chicken anterior pituitary glands in vitro

1984 ◽  
Vol 102 (2) ◽  
pp. 153-159 ◽  
Author(s):  
T. R. Hall ◽  
S. Harvey ◽  
A. Chadwick
Keyword(s):  
Anterior Pituitary ◽  
Prolactin Secretion ◽  
Prostaglandin E ◽  
Hormone Release ◽  
Growth Hormone Release ◽  
Prolactin Release ◽  
Thyrotrophin Releasing Hormone ◽  
Pituitary Glands ◽  
Stimulation Of

ABSTRACT Pituitary glands and hypothalami from broiler fowl were incubated in medium containing testosterone, and prolactin and GH release were determined. Pituitary glands were also preincubated for 20 h in medium containing testosterone, and then in medium containing various secretagogues. Testosterone inhibited the release of prolactin directly from the pituitary gland in a concentration-related manner. The hypothalamus stimulated the release of prolactin, but by a lesser amount in the presence of testosterone. When pituitary glands were preincubated with testosterone, subsequent release of prolactin was inhibited, except with the highest concentration which stimulated prolactin release. Hypothalamic extract (HE) markedly stimulated prolactin release from control pituitary glands although testosterone-primed glands were less responsive. The stimulation of prolactin release by thyrotrophin releasing hormone (TRH) and prostaglandin E2 (PGE2) was also reduced by preincubation of the pituitary glands with testosterone. Priming with testosterone did not affect the release of GH from pituitary glands alone, but reduced the TRH-, HE- and PGE2-stimulated release of GH. These results demonstrate that testosterone directly inhibits prolactin secretion and reduces the sensitivity of pituitary lactotrophs and somatotrophs to provocative stimuli. J. Endocr. (1984) 102, 153–159

Desensitization of rat anterior pituitary gland to thyrotrophin releasing hormone

1984 ◽  
Vol 101 (1) ◽  
pp. 101-105 ◽  
Author(s):  
M. C. Sheppard ◽  
K. I. J. Shennan
Keyword(s):  
Anterior Pituitary ◽  
Prolactin Secretion ◽  
Normal Medium ◽  
Thyrotrophin Releasing Hormone ◽  
Releasing Hormone ◽  
Pituitary Tissue ◽  
Subsequent Response ◽  
Pituitary Glands ◽  
Prolactin Response

ABSTRACT We have studied the secretion of TSH and prolactin from perifused rat anterior pituitary glands in vitro in response to single pulses of thyrotrophin releasing hormone (TRH) and KCl after prior exposure to TRH. Anterior pituitary fragments were incubated in normal medium or in medium containing 28 nmol TRH/1 for 20 h before perifusion. Thyrotrophin releasing hormone (28 nmol/l), administered as a 3-min pulse, stimulated TSH and prolactin release from control tissue to a peak value four or five times that of basal. After exposure of the pituitary tissue to TRH for 20 h, the subsequent response of TSH to a 3-min pulse of TRH was, however, markedly reduced; in contrast, the prolactin response was not significantly reduced. In a similar series of experiments KCl (60 nmol/l) was administered to both control and TRH-'treated' pituitary tissue as a 3-min pulse; no significant differences in TSH responses or prolactin responses were observed. These data indicate that TRH desensitizes the pituitary thyrotroph to a subsequent TRH stimulus but has very little effect on prolactin secretion. J. Endocr. (1984) 101, 101–105

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.

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