THYROTROPHIN RELEASING HORMONE-INDUCED GROWTH HORMONE AND PROLACTIN RELEASE: PHYSIOLOGICAL STUDIES IN INTACT RATS AND IN HYPOPHYSECTOMIZED RATS BEARING AN ECTOPIC PITUITARY GLAND

1977 ◽  
Vol 72 (3) ◽  
pp. 301-311 ◽  
Author(s):  
A. E. PANERAI ◽  
IRIT GIL-AD ◽  
DANIELA COCCHI ◽  
V. LOCATELLI ◽  
G. L. ROSSI ◽  
...  
Keyword(s):  
Pituitary Gland ◽  
Anterior Pituitary ◽  
Time Lapse ◽  
Anterior Pituitary Gland ◽  
Plasma Prolactin ◽  
Thyrotrophin Releasing Hormone ◽  
Releasing Hormone ◽  
Clear Cut ◽  
Urethane Anaesthesia ◽  
Releasing Effect

SUMMARY To determine how the sensitivity of the ectopic anterior pituitary gland to the GH-releasing effect of thyrotrophin releasing hormone (TRH) might be affected by the time lapse from transplantation, TRH (0·15 and 0·6 μg) was injected i.v. into hypophysectomized (hypox)-transplanted rats under urethane anaesthesia 1,3, 8,15, 30 and 60 days after transplantation, and plasma samples were taken 5 and 10 min later. Baseline GH values gradually decreased with time from about 16·0 ng/ml (1 day) to about 3·0 ng/ml (30 and 60 days). The TRH-induced GH release was absent 1 day after transplantation, present only with the higher TRH dose 3 and 8 days after transplantation, and clearly elicitable, also with the lower TRH dose (0·15 μg), from 15 up to 60 days. Determination of plasma prolactin concentrations showed a decline from about 85·0 ng/ml (1 day) to about 32·0 ng/ml (8 days); subsequently (15–60 days) prolactin values stabilized. Plasma prolactin levels increased 15 and 60 days after transplantation only when a dose of 0·6 μg TRH was given. In intact weight-matched rats, TRH induced a GH response only at the dose of 1·2 μg while a short-lived but clear-cut prolactin response could be obtained even with the 0·3 μg dose. The present results indicate that: (1) disconnexion between the central nervous system and the anterior pituitary gland greatly enhances GH responsiveness while blunting prolactin responsiveness to TRH; (2) the sensitivity of the anterior pituitary gland to the GH-releasing effect of TRH increases with time from transplantation; (3) TRH is a more effective prolactin-than GH-releaser on the pituitary gland in situ.

Pro-oestrous-specific role for polyamines in mediating the secretion of prolactin induced by thyrotrophin-releasing hormone in the rat

1993 ◽  
Vol 137 (1) ◽  
pp. 133-139 ◽  
Author(s):  
G. A. Wynne-Jones ◽  
A. M. Gurney
Keyword(s):  
Pituitary Gland ◽  
Anterior Pituitary ◽  
Prolactin Secretion ◽  
Anterior Pituitary Gland ◽  
Oestrous Cycle ◽  
Male Rats ◽  
Pituitary Cells ◽  
Plasma Prolactin ◽  
Thyrotrophin Releasing Hormone ◽  
Releasing Hormone

ABSTRACT The activity of ornithine decarboxylase (ODC) in the rat anterior pituitary gland varies during the oestrous cycle, with a rise in activity seen at pro-oestrus. This enzyme, which is rate-limiting for the synthesis of the polyamines, can be specifically and irreversibly blocked by α-difluoromethylornithine (DFMO). A previous study showed that when this drug was administered to rats in vivo on the afternoon of pro-oestrus, it suppressed the normal surge in plasma prolactin levels that occurred later that day. The effect of DFMO was associated with reduced levels of putrescine in the anterior pituitary gland, suggesting that ODC activity in the lactotroph might be involved in the prolactin surge. We have examined the effects of DFMO on the secretion of prolactin from anterior pituitary cells, isolated either from male rats or from females at different stages of the oestrous cycle. The drug was found to reduce prolactin secretion stimulated by thyrotrophin-releasing hormone (TRH), but only in cells isolated from pro-oestrous animals and only for 2 days after cell isolation. Basal secretion was unaffected by DFMO. The results imply that ODC is important for TRH-stimulated prolactin secretion at pro-oestrus, and it is specific for pro-oestrus. The prolactin surge could therefore be influenced by this ODC-dependent effect of TRH. The pro-oestrous-specific response to TRH may be a consequence of the increased ODC activity seen at this time. Alternatively, the increased ODC activity could be a consequence of coupling to TRH receptors, which are known to increase in number at pro-oestrus. Journal of Endocrinology (1993) 137, 133–139

Ornithine decarboxylase activity and polyamines in the anterior pituitary gland during the rat oestrous cycle

1985 ◽  
Vol 107 (1) ◽  
pp. 83-87 ◽  
Author(s):  
L. Persson ◽  
M. Nilsson ◽  
E. Rosengren
Keyword(s):  
Pituitary Gland ◽  
Ornithine Decarboxylase ◽  
Anterior Pituitary ◽  
Anterior Pituitary Gland ◽  
Oestrous Cycle ◽  
Ovariectomized Rats ◽  
Oestrogen Treatment ◽  
Thyrotrophin Releasing Hormone ◽  
Releasing Hormone ◽  
Lh Releasing Hormone

ABSTRACT The biosynthesis of polyamines, an ubiquitous group of amines shown to be essential for normal cellular growth and differentiation, was studied in the rat anterior pituitary gland during the different stages of the oestrous cycle. The activity of ornithine decarboxylase (ODC), which catalyses the rate-limiting step in the biosynthesis of polyamines, was low during oestrus, metoestrus and dioestrus. However, a marked transitory rise in ODC activity was found in the pituitary gland on the evening of pro-oestrus. The rise in ODC activity was accompanied by an increase in the pituitary content of the polyamines putrescine and spermidine. Ovariectomy did not significantly change the basal ODC activity in the pituitary gland. Oestrogen treatment of ovariectomized rats resulted in a marked stimulation of pituitary polyamine biosynthesis. The largest effects were observed when oestrogen was given as two injections 72 h apart, which gave rise to levels of ODC activity comparable to those observed on the evening of pro-oestrus. The increase in polyamine synthesis in the anterior pituitary gland during pro-oestrus appeared not to be related to the preovulatory secretion of LH or prolactin, since neither LH-releasing hormone nor thyrotrophin-releasing hormone (which induces a secretion of prolactin) affected pituitary ODC activity. The observed biosynthesis of polyamines may be associated with the cellular proliferation which occurs in the anterior pituitary gland at oestrus. J. Endocr. (1985) 107, 83–87

Alteration by thyrotrophin-releasing hormone of heterogeneous components associated with thyrotrophin biosynthesis in the rat anterior pituitary gland

1984 ◽  
Vol 103 (2) ◽  
pp. 165-171 ◽  
Author(s):  
M. Mori ◽  
M. Murakami ◽  
T. Iriuchijima ◽  
H. Ishihara ◽  
I. Kobayashi ◽  
...  
Keyword(s):  
Protein Synthesis ◽  
Pituitary Gland ◽  
Anterior Pituitary ◽  
De Novo ◽  
Close Association ◽  
Anterior Pituitary Gland ◽  
Male Rats ◽  
Thyrotrophin Releasing Hormone ◽  
Releasing Hormone ◽  
Pituitary Glands

ABSTRACT An influence of thyrotrophin-releasing hormone (TRH) on TSH heterogeneity in close association with de-novo biosynthesis was studied in rat anterior pituitary glands. Hemipituitary glands from adult male rats were incubated in Krebs–Henseleit–glucose media containing [3H]glucosamine and [14C]alanine for 3 and 6 h in the presence or absence of 10 ng TRH per ml. Fractions of TSH in the pituitary extracts were obtained using affinity chromatography coupled with an anti-rat TSH globulin. These TSH fractions were analysed by isoelectric focusing. The control pituitary glands were composed of four component peaks (isoelectric point (pI) 8·7, 7·8, 5·3 and 2·5) of [3H]glucosamine and [14C]alanine incorporated into TSH, and the amounts of radioactivity of these components were increased with the incubation time. Of these peaks, radioactive components of pI 8·7 and 7·8 coincided with the non-radioactive TSH components measured by radioimmunoassay. Addition of TRH increased incorporation of [14C]alanine into TSH in each of the components to a greater extent than that of [3H]glucosamine. In addition, new components with pI 7·2, 6·5 and 6·2, each component corresponding to each unlabelled TSH component, were demonstrated in the presence of TRH. Because addition of TRH did not change the amounts of [14C]alanine-labelled TSH in the media, the newly formed components were assumed to be connected with protein synthesis occurring in the anterior pituitary gland, which may be specific substances in response to TRH administration. These results indicate that TRH principally elicits an increase in protein synthesis in TSH at the anterior pituitary level, resulting in an alteration of TSH heterogeneity. J. Endocr. (1984) 103, 165–171

Pituitary and testicular responses in sexually mature bulls after intravenous injections of graded doses of LH-releasing hormone

1984 ◽  
Vol 103 (3) ◽  
pp. 371-376 ◽  
Author(s):  
M. J. D'Occhio ◽  
B. P. Setchell
Keyword(s):  
Pituitary Gland ◽  
Anterior Pituitary ◽  
Anterior Pituitary Gland ◽  
Limiting Factor ◽  
Releasing Hormone ◽  
Intravenous Injections ◽  
Gonadotrophin Secretion ◽  
Lh Release ◽  
Lh Releasing Hormone ◽  
Sexually Mature

ABSTRACT The capacity of the anterior pituitary gland and testes in mature bulls (705±9 (s.e.m.) kg body wt, n = 4) to respond to graded doses of LH-releasing hormone (LHRH) was assessed relative to endogenous profiles of LH and testosterone secretion. Endogenous hormone profiles were determined by bleeding bulls at 20-min intervals for 12 h. Responses to LHRH were assessed on successive days after single intravenous injections of 1, 5, 10, 50 or 100 ng LHRH/kg body wt. Blood samples were taken at −40, −20, 0, 10, 20, 30, 40, 60 and 120 min relative to LHRH injection. During a 12-h bleed bulls showed spontaneous pulses of LH and testosterone which had peak amplitudes of 2·6±0·5 μg/l and 44·5 ± 7·1 nmol/l respectively. Respective peak LH (μg/l) and testosterone (nmol/l) responses to LVRH were as follows: 1 ng LHRH (3·0±0·7: 47·3±4·1); 5 ng LHRH (8·0±1·2; 52·8 ± 6·2); 10 ng LHRH (11·1±2·3; 57·7 ± 9·1); 50 ng LHRH (19·2±2·8; 47·9±8·6); 100 ng LHRH (19·1±4·7; 43·9 ±6·4). A dose of 1 ng LHRH/kg produced LH and testosterone responses which were comparable in amplitude to spontaneous peaks in the respective hormone. There was a linear (y = 0·28x+5·72; r = 0·81) increase in the LH response to doses of LVRH between 1 and 50 ng/kg; corresponding testosterone responses showed no relationship with the dose of LHRH. The capacity of the anterior pituitary gland to release amounts of LH eight to ten times in excess of those secreted during spontaneous peaks suggests that (1) there exists a large releasable store of LH in the anterior pituitary gland and (2) hypothalamic LHRH is a limiting factor in gonadotrophin secretion. In contrast to LH release, the androgenic response of the testes to acute gonadotrophic stimulation is determined largely by prevailing steroidogenic activity. J. Endocr. (1984) 103, 371–376

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