Interaction between the α2-adrenergic system and nursing in the regulation of growth hormone secretion in the neonatal rat

Abstract

Kacsóh B, Opp JS, Crowley WR, Grosvenor CE. Interaction between the a2-adrenergic system and nursing in the regulation of growth hormone secretion in the neonatal rat. Acta Endocrinol 1993;128:184-91. ISSN 0001-5598 Separation of neonatal rats from their mothers decreases, while a subsequent period of suckling (nursing) increases, serum growth hormone (GH) levels in neonatal rats. Milk-borne (humoral) factors and neural factors inherent in mother-offspring interaction have been implicated in these phenomena. Conflicting reports have demonstrated the \g=a\2-adrenergic agonist clonidine to increase and to decrease serum GH levels in 10-day-old rats. The present experiments were aimed at testing whether an interaction between the \g=a\2-adrenergic system and the nursing-induced changes in GH secretion could account for the discrepancy. Rat pups were treated with clonidine (150 \g=m\g/kg) or the \g=a\2-adrenergic antagonist yohimbine (10 mg/kg), and the drug treatment was combined with separation of the mothers and nursing. Yohimbine did not affect serum GH levels in separated two-day-old pups (i.e. basal levels of the hormone), but prevented the nursing-induced increase in serum GH concentration. In twoday-old pups, clonidine had no effect on basal GH levels but, like yohimbine, prevented the increase in serum GH normally associated with nursing. Both yohimbine and clonidine prevented active sucking behavior, i.e. the pups did not search for and/or attach to the nipples of their mothers. Moreover, the pups treated with yohimbine and clonidine were cooler to the touch than the littermate controls. In eight-day-old pups, yohimbine prevented the nursing-induced increase in serum GH and decreased GH levels below the saline-injected, separated control. As in two-day-old pups, clonidine prevented the suckling-induced release of GH and failed to induce GH-release above that of saline-injected, separated pups. By day 10 postpartum. clonidine became capable of stimulating GH release, but only in separated male pups. The effects of CLO and nursing in male pups were not additive: either treatment alone was as

The effect of α2 adrenoceptor blockers on aggressive behavior in mice: implications for the actions of adrenoceptor agents

“…The contradiction (i.e. similar effects after ~2 adrenoceptor agonists and antagonists) seems to be reproducible, since clonidine and yohimbine have shown similar effects in a variety of behavioral investigations (Ferrari et al 1991;Matsumoto et al 1991;Cutler 1993;Kacsoh et al 1993).…”

Signaling mechanisms for α2-adrenergic inhibition of PACAP-induced growth hormone secretion and gene expression grass carp pituitary cells

“…This stimulatory effect is mediated through ␣ 2 -adrenoreceptors expressed in the hypothalamus (12), activation of which can stimulate GHRH secretion from the arcuate nucleus (10) with simultaneous inhibition on SRIF release from the periventricular nucleus (30). In the rat, ␣ 2 stimulation of GH release is sexually dimorphic (9), age-dependent (25), and plays a role in regulating GH pulsatility in vivo (28). In the same animal model, norepinephrine (NE) and epinephrine (Ep) can be detected in the hypophyseal portal blood (24,54), suggesting that adrenergic input may have direct effects at the pituitary level.…”