Inhibitory effect of the alpha 1-adrenergic antagonist prazosin on food intake in pygmy goats

Effect of the H1-histamine receptor agonist betahistine on drinking and eating behavior in pygmy goats

The effect of different doses of the H1-receptor agonist betahistine (0.9 and 2, 4 and 8 mg/kg b.wt.(0.75)) on water and food intake was investigated in 12 pygmy goats. Intraperitoneal (i.p.) injection of betahistine (2, 4, and 8 mg/kg b.wt.(0.75)) stimulated drinking in a dose-dependent manner. Food intake was decreased after the injection of 4 or 8 mg/kg b.wt.(0.75) betahistine, respectively. The increase in water intake was characterized by an increased draft size and decreased latency to drink. The decrease in food intake at the highest dose tested was characterized by an increased latency to eat and by a decreased meal frequency, and food intake associated to drinking was decreased. In line with previous studies, these results support the hypothesis that food-associated drinking is mediated by stimulation of H1-receptors of histamine in pygmy goats.

Stimulation of food intake by xylazine in sheep

The effect of xylazine (0.05 and 0.15 mg/kg, intramuscularly) on food (concentrate) intake was examined in ewes. Xylazine at 0.15 mg/kg significantly increased the 2 and 24 h food intake in comparison with control values. Xylazine treatments significantly and dose-dependently decreased the heart rate, respiratory rate and ruminal motility, and increased the rectal temperature when compared with pretreatment values. The changes in the physiological variables and the slight tranquilizing effect of xylazine apparently did not interfere with the food intake. The data suggest that xylazine increases food intake in freely feeding sheep.

Opposite effects on hippocampal corticosteroid receptors induced by stimulation of beta and alpha 1 noradrenergic receptors

Central corticosteroid receptors play an important role in the regulation of the secretion of corticosterone. Although these receptors are thought to be regulated by circulating levels of corticosterone, there is evidence for direct neural control. For example, it has been shown that noradrenergic lesions can both increase and decrease corticosteroid receptors depending on the brain structure involved. In the present study, we investigated the role of different noradrenergic receptors in the rat, by examining the effect of the acute administration of agonists and antagonists of beta and alpha 1 noradrenergic receptors on hippocampal type I and type II corticosteroid receptor levels. The effects of these drugs were studied in adrenalectomized animals whose plasma levels of corticosterone were maintained in the physiological range by implantation of coritcosterone pellets. Our results show that the beta receptor agonist salbutamol (5 mg/kg) increased the number of type I and type II hippocampal corticosteroid receptors. This effect was blocked by the beta receptor antagonist propranolol (5 mg/kg), which had no effect on its own. In contrast, the alpha 1 receptor agonist phenylephrine (100 micrograms) reduced the number of type I and type II corticosteroid receptors, whereas the alpha 1 receptor antagonist prazosin (0.5 mg/kg) increased type I receptors. The effect of prazosin was attributed to an increase in the relative beta tonus resulting from blockade of alpha 1 receptors. Its effect was reversed by the simultaneous injection of the beta receptor antagonist propranolol. In conclusion, our results show that noradrenergic transmission can have both a facilitatory and an inhibitory action on central corticosteroid receptors by acting respectively on beta and alpha 1 noradrenergic receptors.(ABSTRACT TRUNCATED AT 250 WORDS)

Vasopressin inhibits food intake in pygmy goats by activation of alpha 1-adrenergic receptors

The hypophagic effect of intraperitoneally injected VP (1.5 micrograms/kg) was blocked by concomitant injection of the alpha 1-adrenergic antagonist prazosin (27 and 40 micrograms/kg). Both the alpha 2-adrenergic antagonists idazoxan (300 micrograms/kg) and yohimbine (500 micrograms/kg) and the beta-adrenergic antagonist propranolol (500 micrograms/kg) failed to block the hypophagia induced by VP (1.5 micrograms/kg). The results suggest that the hypophagic effect of VP is mediated by alpha 1-adrenergic receptors.