PLASMA CONCENTRATIONS OF PROLACTIN AND THYROTROPHIN DURING SUCKLING IN URETHANE-ANAESTHETIZED RATS

1976 ◽  
Vol 70 (3) ◽  
pp. 429-437 ◽  
Author(s):  
F. R. BURNET ◽  
J. B. WAKERLEY
Keyword(s):  
Plasma Concentrations ◽  
Fold Increase ◽  
Prolactin Release ◽  
Thyrotrophin Releasing Hormone ◽  
Releasing Hormone ◽  
Pressure Application ◽  
Oxytocin Release ◽  
Anaesthetized Rats ◽  
Substantial Change ◽  
Anaesthetized Rat

SUMMARY Plasma levels of prolactin and TSH were determined by radioimmunoassay in urethane-anaesthetized lactating rats during suckling. Oxytocin release was monitored by recording intramammary pressure. Application of ten pups, 3 h after administration of urethane (1·1 g/kg, i.p.), evoked a parallel rise in prolactin and TSH concentrations which reached a maximum during the 3rd hour of suckling and then declined. Peak hormone concentrations represented a 25-fold increase in prolactin and a ten-fold increase in TSH. Suckling also elicited a pulsatile (every 5–10 min) release of 0·5–1·0 mu. oxytocin. The gradual rise in prolactin and TSH occurred between the 1st and 20th oxytocin pulses. Intravenous injection of thyrotrophin-releasing hormone (TRH) into unsuckled, anaesthetized lactating rats resulted in a 7- to 30-fold increase in TSH concentration, whereas prolactin levels showed no substantial change. These results indicate that suckling releases TSH as well as prolactin in the urethane-anaesthetized rat. However, the absence of prolactin release after injections of TRH makes it unlikely that both endocrine responses are regulated solely by the actions of this one releasing hormone.

PLASMA CONCENTRATIONS OF PROLACTIN AND THYROTROPHIN DURING SUCKLING: EFFECTS OF STIMULATION OF THE MEDIAN EMINENCE

1978 ◽  
Vol 76 (3) ◽  
pp. 557-558 ◽  
Author(s):  
J. B. WAKERLEY ◽  
M. B. TER HAAR
Keyword(s):  
Direct Effect ◽  
Median Eminence ◽  
Plasma Concentrations ◽  
Prolactin Release ◽  
Thyrotrophin Releasing Hormone ◽  
Releasing Hormone ◽  
Animal Physiology ◽  
Inhibiting Factor ◽  
Hypothalamic Level ◽  
Stimulation Of

A.R.C. Institute of Animal Physiology, Babraham, Cambridge, CB2 4AT (Received 1 November 1977) Thyrotrophin releasing hormone (TRH) can have a stimulatory effect on the release of both prolactin and thyrotrophin (TSH; Deis & Alonso, 1973), although in the rat, supraphysiological doses of TRH are required to affect the secretion of prolactin (Burnet & Wakerley, 1976). A more important factor in the control of the release of prolactin is considered to be prolactin release inhibiting factor (PIF), which is thought to act through the catecholamine, dopamine (MacLeod, 1976). Stimuli which cause the concomitant release of TSH and prolactin are thought to have a direct effect at the hypothalamic level such that neurones releasing TRH are excited, whereas those releasing PIF are inhibited. In the present work, we have tested this hypothesis using the suckling stimulus to elicit the simultaneous release of prolactin and TSH (Blake, 1974; Burnet & Wakerley, 1976). If

Effects of infusion of thyrotrophin releasing hormone and dopamine either alone or in combination on plasma prolactin concentrations in the anoestrous ewe

1983 ◽  
Vol 96 (2) ◽  
pp. 353-357
Author(s):  
B. F. Fitzgerald ◽  
F. J. Cunningham
Keyword(s):  
Combined Treatment ◽  
Plasma Concentrations ◽  
Regulatory Role ◽  
Plasma Prolactin ◽  
Thyrotrophin Releasing Hormone ◽  
Releasing Hormone

Plasma concentrations of prolactin in anoestrous ewes were respectively lowered or raised by the separate infusion of dopamine or thyrotrophin releasing hormone (TRH). Combined treatment with dopamine and TRH lowered the concentration of prolactin in plasma but the values increased markedly after the treatment was stopped and reached a level equivalent to that found in ewes treated with TRH alone. The results are interpreted as evidence that both dopamine and TRH play a regulatory role in determining the secretion of prolactin in the ewe.

THE INFLUENCE OF OESTROGEN ADMINISTRATION IN VIVO ON IN VITRO PROLACTIN RELEASE

1979 ◽  
Vol 92 (3) ◽  
pp. 437-447 ◽  
Author(s):  
Sandford Jaques ◽  
Richard R. Gala
Keyword(s):  
Time Of Day ◽  
Ovariectomized Rat ◽  
Prolactin Release ◽  
Thyrotrophin Releasing Hormone ◽  
Releasing Hormone ◽  
Stable Pool ◽  
Releasable Pool ◽  
Storage Pools

ABSTRACT The influence of oestrogen administered to the ovariectomized rat on the interaction between dopamine (DA) and thyrotrophin releasing hormone (TRH) on the release of radioimmunoassayable (RIA) and [3H] leucine incorporated into prolactin ([3H]PRL) was examined in vitro. Dopamine had a more marked suppressing effect on newly synthetized PRL (80 %), as determined [3H]PRL, than on total PRL (50 %), as determined by RIA-PRL. The administration of 5 μg of oestradiolbenzoate (OeB) for 7 days resulted in blocking the suppressing effect of DA when RIA-PRL was measured but not when [3H]PRL was measured. The administration of 5 μg of OeB enabled TRH to partially override the suppressing effect of DA and the degree of response was more marked when RIA-PRL was measured than when [3H]PRL was measured. The administration of 50 μg of OeB for 3 days enabled TRH to override the DA blockade of prolactin release to levels comparable to that of the control when RIA-PRL was measured but had little to no effect on [3H]PRL. The results are discussed in relation to the two storage pools of PRL in the pituitary and the data suggest that DA acts predominantly to suppress the newly synthetized, rapidly releasable pool. Oestrogen acts to block DA action on the older more stable PRL pool. The ability of TRH to override the DA blockade of PRL release depends upon the presence of oestrogen; here TRH acts predominantly on the older more stable pool of PRL. Oestrogen's action on disrupting the DA suppression of PRL release appears to be related to the time of day the hormone is administered subsequent to when the pituitary is exposed to DA in vitro.

EVIDENCE FOR THE INVOLVEMENT OF HYPOTHALAMIC DOPAMINE AND THYROTROPHIN-RELEASING HORMONE IN SUCKLING-INDUCED RELEASE OF PROLACTIN

1981 ◽  
Vol 91 (2) ◽  
pp. 213-223 ◽  
Author(s):  
W. J. DE GREEF ◽  
T. J. VISSER
Keyword(s):  
Nerve Stimulation ◽  
Plasma Levels ◽  
Plasma Prolactin ◽  
Prolactin Release ◽  
Thyrotrophin Releasing Hormone ◽  
Dopamine Infusion ◽  
Releasing Hormone ◽  
Peripheral Plasma ◽  
Transient Decrease ◽  
Hypothalamic Dopamine

The changes in adenohypophysial and hypothalamic content and in hypothalamic release of dopamine and thyrotrophin-releasing hormone (TRH) into the hypophysial portal system during the suckling-induced release of prolactin were investigated. An increase in peripheral plasma levels of prolactin was induced by mammary nerve stimulation in urethane-anaesthetized and by suckling in unanaesthetized lactating rats. In the unanaesthetized rat, suckling caused a decrease of dopamine levels in hypothalamus and adenohypophysis and a short-lasting small increase in hypothalamic TRH. Mammary nerve stimulation induced a transient decrease in dopamine levels and an increase in TRH levels in hypophysial stalk blood. To assess the significance of the observed changes in dopamine and TRH levels for prolactin release, these changes in dopamine and TRH were mimicked in lactating rats anaesthetized with urethane and pretreated with α-methyl-p-tyrosine (AMpT, a competitive inhibitor of catecholamine synthesis). Reducing hypothalamic dopamine secretion by treatment with AMpT increased peripheral plasma levels of prolactin from 15 to 477 ng/ml; an infusion with dopamine, resulting in plasma levels similar to those measured in hypophysial stalk plasma, reduced plasma levels of prolactin to 127 ng/ml. Neither a 50% reduction in dopamine infusion rate for 15 min nor administration of 100 ng TRH caused an appreciable change in plasma prolactin levels. However, when dopamine infusion was reduced by 50% for 15 min just before TRH was injected, then an increase in plasma levels of prolactin from 172 to 492 ng/ml was observed. Thus, the effectiveness of TRH in releasing prolactin in the lactating rat was enhanced when a transient decrease of dopamine levels occurred before treatment with TRH. It is concluded that the changes observed in dopamine and TRH levels in hypophysial stalk blood are involved in the suckling-induced prolactin release in an important manner.

Effects of antiserum to thyrotrophin-releasing hormone on the concentrations of plasma prolactin, thyrotrophin and LH in the pro-oestrous rat

1985 ◽  
Vol 104 (2) ◽  
pp. 205-209 ◽  
Author(s):  
A. M. Horn ◽  
H. M. Fraser ◽  
G. Fink
Keyword(s):  
Plasma Concentrations ◽  
Passive Immunization ◽  
Immune Serum ◽  
Female Rats ◽  
Plasma Prolactin ◽  
Thyrotrophin Releasing Hormone ◽  
Blood Samples ◽  
Releasing Hormone ◽  
Sheep Blood

ABSTRACT The possible role of thyrotrophin-releasing hormone (TRH) in causing the pro-oestrous surge of prolactin was investigated in conscious female rats by passive immunization with a specific anti-TRH serum raised in sheep. Blood samples were withdrawn through a previously implanted intra-atrial cannula. The i.p. injection of 1 ml anti-TRH serum, but not non-immune sheep serum, at 13.00 h of pro-oestrus delayed by about 1 h the onset of the prolactin surge, but the peak of the surge was similar to that in animals injected with the non-immune serum. The plasma concentrations of TSH were significantly reduced by the anti-TRH serum, but plasma concentrations of LH were not significantly affected. These results show that TRH may play an important role in the timing and initiation, but not the maintenance of the prolactin surge in the pro-oestrous rat. J. Endocr. (1985) 104, 205–209

Prolactin release in man: influence of cimetidine, thyrotrophin-releasing hormone and acute hypercalcaemia

1983 ◽  
Vol 102 (4) ◽  
pp. 481-485 ◽  
Author(s):  
Sven Röjdmark
Keyword(s):  
Prolactin Level ◽  
Anterior Pituitary ◽  
Serum Prolactin ◽  
Healthy Individuals ◽  
Serum Prolactin Level ◽  
Prolactin Release ◽  
Thyrotrophin Releasing Hormone ◽  
Releasing Hormone ◽  
Pre Treatment ◽  
Acute Changes

Abstract. The responsiveness of anterior pituitary lactotrophs and thyrotrophs to cimetidine (Cim) was investigated in healthy volunteers. Four-hundred mg Cim, injected iv, raised the serum prolactin level (Prl) from 14 ± 2 to 58 ± 9 ng/ml (P < 0.001), but left the serum thyrotrophin level (TSH) unaffected. Acute hypercalcaemia, induced by iv infusion of calcium, blunted this Cim-elicited Prl response by 35 ± 4% (P < 0.01). Iv injection of 25 μg thyrotrophin-releasing hormone (TRH) had similar Prl-releasing potency as 400 mg Cim, and raised the Prl level from 14 ± 1 to 51 ± 6 ng/ml (P < 0.001). In contrast to Cim, TRH also increased the TSH level significantly. Although oral pre-treatment with Cim for 3 days (1000 mg/day) failed to affect the Prl response to TRH in this study, iv injection of the drug more than doubled the above mentioned Prl response to TRH. The TSH response to TRH remained unaffected both by oral and by iv administration of Cim. These results imply that acute changes in serum calcium affect the release pattern of Prl, and that iv administration of Cim may add Prl-releasing power to TRH in healthy individuals.

Effects of prednisone on thyroid and gonadal endocrine function in dogs

1983 ◽  
Vol 96 (2) ◽  
pp. 293-NP ◽  
Author(s):  
R. J. Kemppainen ◽  
F. N. Thompson ◽  
M. D. Lorenz ◽  
J. F. Munnell ◽  
P. K. Chakraborty
Keyword(s):  
Hormone Secretion ◽  
Plasma Concentrations ◽  
Thyroid Tissue ◽  
Endocrine Function ◽  
Follicular Cell ◽  
Electron Microscopic ◽  
Thyrotrophin Releasing Hormone ◽  
Releasing Hormone ◽  
Prednisone Treatment ◽  
Basal Plasma

To assess the effect of a glucocorticoid on thyroid and gonadal endocrine function, prednisone was administered on alternate days to dogs. The prednisone injections resulted in adrenocortical suppression, as shown by the response to ACTH. Basal plasma thyroxine and tri-iodothyronine concentrations were considerably reduced in prednisone-treated dogs. However, the thyroid response to injection of thyrotrophin-releasing hormone was not altered, indirectly demonstrating that pituitary release of TSH was not inhibited by prednisone. Similarly, the response of the thyroid to exogenous TSH was not reduced by prednisone treatment. Electron microscopic examination of thyroid tissue revealed accumulation of colloid droplets in the follicular cell cytoplasm of dogs treated with prednisone. It is postulated that prednisone may interfere with basal thyroid hormone secretion by inhibiting lysosomal hydrolysis of colloid in the thyroid follicular cell. Basal plasma concentrations of LH and testosterone, measured in the male dogs, were reduced by prednisone treatment. Responses of prednisone-treated dogs to luteinizing hormone releasing hormone were not significantly reduced. Prednisone administration did not alter testicular responsiveness to injection of human chorionic gonadotrophin. After orchidectomy, plasma LH values were significantly reduced in prednisone-treated dogs. Taken together, these results suggest that LH secretion in dogs is inhibited at the hypothalamic and/or pituitary level by prednisone administration, which consequently results in reduced testosterone concentrations.

DIFFERENTIAL SENSITIVITY OF PROLACTIN RELEASE TO DOPAMINE AND THYROTROPHIN-RELEASING HORMONE IN INTACT AND PITUITARY STALK-SECTIONED RHESUS MONKEYS

1980 ◽  
Vol 84 (3) ◽  
pp. 479-487 ◽  
Author(s):  
R. L. NORMAN ◽  
S. K. QUADRI ◽  
H. G. SPIES
Keyword(s):  
Rhesus Monkeys ◽  
Differential Sensitivity ◽  
Pituitary Stalk ◽  
Serum Prolactin ◽  
Prolactin Release ◽  
Thyrotrophin Releasing Hormone ◽  
Releasing Hormone ◽  
Basal Serum ◽  
Hypothalamic Influence ◽  
Higher Doses

The effects of dopamine and thyrotrophin-releasing hormone (TRH) on prolactin release was studied in 14 intact and six pituitary stalk-sectioned (SS) female rhesus monkeys (Macaca mulatta). Baseline prolactin values were ninefold higher in SS animals (149 ± 16 ng/ml) than in intact animals (16 ± 1 ng/ml). Prolactin release after intravenous administration of TRH in doses of 0,125,250, 500 and 1000 ng revealed that SS monkeys were more sensitive to the prolactin-releasing activity of this tripeptide than were intact animals. A significant (P < 0·05) increment in serum prolactin was observed in SS animals after injection of 125 ng TRH whereas 250 ng was required to raise prolactin levels in the circulation of intact animals significantly (P <0·05). Furthermore, at each comparable dose level of TRH, the increment in serum prolactin was distinctly greater in SS animals than in intact monkeys. Infusion of dopamine at the rate of 10 μg/kg body weight per min significantly (P <0·05) lowered prolactin levels within 60 min in intact animals and no further decline was observed with 20 or 40 μg dopamine. Serum prolactin concentrations were not affected by saline infusion or by 5 μg dopamine. Infusion of dopamine at the rate of 10 μg/kg body wt per min also resulted in significant (P <0·01) suppression of serum prolactin in SS animals. This prolactin decrease was apparent within 40 min. Prolactin release after 500 ng TRH was less in these dopamine-treated SS monkeys than after an infusion of saline. Higher doses of dopamine (20 and 40 μg) did not cause a further decrease in basal serum prolactin concentrations, but these two dopamine treatments blocked the increase in prolactin elicited by 500 ng TRH. The results suggest that the removal of hypothalamic influence, possibly related to the effects of dopamine, renders the pituitary gland more sensitive to the prolactin-releasing action of TRH.

Preferential release of tri-iodothyronine following stimulation by thyrotrophin or thyrotrophin-releasing hormone in sheep of different ages

1992 ◽  
Vol 132 (1) ◽  
pp. 93-100 ◽  
Author(s):  
R. Peeters ◽  
N. Buys ◽  
D. Vanmontfort ◽  
J. Van Isterdael ◽  
E. Decuypere ◽  
...  
Keyword(s):  
Thyroid Gland ◽  
Thyroid Hormones ◽  
Plasma Concentrations ◽  
Thyrotrophin Releasing Hormone ◽  
Releasing Hormone ◽  
Neonatal Injection ◽  
Different Ages ◽  
Neonatal Lambs

ABSTRACT The influence of TRH and TSH injections on plasma concentrations of tri-iodothyronine (T3) and thyroxine (T4) was investigated in neonatal (injection within 0·5 h after delivery) and growing lambs and in normal, pregnant and lactating adult ewes (all 2 years old and originating from Suffolk, Milksheep and Texal cross-breeds). Neonatal lambs had higher levels of T3, T4 and GH compared with all other groups, whereas prolactin and TSH were higher in lactating ewes. In all animals, injections of TRH increased plasma concentrations of prolactin and TSH after 15 min but not of GH at any time. Small increases in T3 and T4 were observed in neonatal lambs, without any effect on the T3 and T4 ratio, after prolactin administration, whereas prolactin did not influence plasma concentrations of T3 or T4 in all other experimental groups. Similar results for thyroid hormones were obtained after TRH or TSH injections. It was therefore concluded that the effects observed after TRH challenge were mediated by the release of TSH. With the possible exception of neonatal lambs, plasma concentrations of T3 after administration of TRH or TSH were always increased before those of T4; the increase in T3 occurred within 0·5–1 h compared with 2–4 h for T4 in all experimental groups. This resulted in an increased ratio of plasma T3 to T4 up to 4 h after injection. It is concluded that, in sheep, TRH and TSH preferentially release T3 from the thyroid gland probably by a stimulatory effect of TSH on the intrathyroidal conversion of T3 to T4. Journal of Endocrinology (1992) 132, 93–100

scholarly journals Prolactin release in response to nursing or milking stimulus in the ewe. Is it mediated by thyrotrophin releasing hormone ?

1977 ◽  
Vol 17 (3B) ◽  
pp. 441-452 ◽  
Author(s):  
G. KANN ◽  
R. HABERT ◽  
Chantal MEUSNIER ◽  
Hélène Sophie RYNIEWICZ
Keyword(s):  
Prolactin Release ◽  
Thyrotrophin Releasing Hormone ◽  
Releasing Hormone
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