Effects of Neonatal Treatment with Monosodium Glutamate on Growth Hormone Release Induced by Clonidine and Prostaglandin E₁ in Conscious Male Rats

Abstract

Effects of the centrally acting α-adrenergic agonist, clonidine, on growth hormone (GH) secretion was studied in conscious male rats pretreated with monosodium glutamate (MSG) during the neonatal period. GH secretory profiles in individual adult rats were obtained by repeated blood samplings every 10–20 min from 10.00 to 17.00 h. GH secretion was pulsatile with mean peak values at around 12.40 and 15.20 h in control rats. When clonidine (15 µg/100 g body weight) was injected intravenously into control rats at 14.00 h in the interval between two anticipated spontaneous GH bursts, plasma GH was increased with a mean peak value 20 min after the injection, and the following anticipated spontaneous GH burst was not observed during the experiment. In the rats neonatally treated with MSG (4 mg/g body weight, s.α), which causes selective destruction of the hypothalamic arcuate nucleus, plasma GH response to clonidine as well as the spontaneous GH bursts were considerably blunted, whereas prostaglandin Ei (5 µg/100 g body weight, i.v.) caused an abrupt increase in plasma GH levels in these animals. These results suggest that clonidine stimulates rat GH secretion, possibly by acting within the hypothalamus to stimulate GH releasing factor neurons.

Effects of Atipamezole, an .ALPHA.2-Adrenergic Antagonist, and Somatostatin on Xylazine-lnduced Growth Hormone Release in Calves.

“…It has been demonstrated that the GH-releasing action of the a2-adrenergic mechanism was mediated through the stimulation of GHRH in the rat [16][17][18][19]. On the other hand, there are some reports which proposed that the stimulatory effect of clonidine, an a2-adrenoceptor agonist, on GH release is mainly exerted by inhibiting the hypothalamic SRIF release in rats [20][21][22] and man [23].…”

Obesity-Associated Decrease in Growth Hormone-Releasing Hormone Gene Expression: A Mechanism for Reduced Growth Hormone mRNA Levels in Genetically Obese Zucker Rats

“…One such agent likely to play a role in GHRH deficiency is norepinephrine. cb-Adrenergic mechanisms stimulate GHRH release [32][33][34], and a decrease in cb-adrenergic tone in response to changed metabolic milieu [35] in the obese rat could con tribute to GHRH deficiency. The observation of de creased norepinephrine levels [36] and increased norepi nephrine binding in the hypothalamus of obese rats [37] supports the possibility of a reduced cb-adrenergic tone in these animals.…”

Comparative study of short‐term anxiolytic potency of alprazolam and tandospirone in psychiatric outpatients with anxiety disorders

“…Alprazolam, as a benzodiazepine, inhibits noradrenergic neurons by activation of GABA A receptors, causing the reduction in the MHPG level. Previous studies have indicated that post-synaptic noradrenaline 2-adrenoreceptors exert a stimulatory in¯uence on the secretion of growth hormone in rats (Eden et al, 1981;Katakami et al, 1984). Another study has reported that alprazolam caused a dose-dependent increase in plasma growth hormone when given alone to rats pretreated with reserpine and that this effect was antagonized by either of the two selective 2-receptor antagonists yohimbine or idazoxane (Elias et al, 1986).…”