Abstract
We have demonstrated that central administration of zinc in minute amounts induces a significant antidipsogenic action in dehydrated rats as well as in rats under central cholinergic and angiotensinergic stimulation. Here we show that acute third ventricle injections of zinc also block water intake induced by central ss-adrenergic stimulation in Wistar rats (190-250 g). Central inhibition of opioid pathways by naloxone reverses the zinc-induced antidipsogenic effect in dehydrated rats. After 120 min, rats receiving third ventricle injections of isoproterenol (160 nmol/rat) exhibited a significant increase in water intake (5.78 +/- 0.54 ml/100 g body weight) compared to saline-treated controls (0.15 +/- 0.07 ml/100 g body weight). Pretreatment with zinc (3.0, 30.0 and 300.0 pmol/rat, 45 min before isoproterenol injection) blocked water intake in a dose-dependent way. At the highest dose employed a complete blockade was demonstrable (0.54 +/- 0.2 ml/100 g body weight). After 120 min, control (NaAc-treated) dehydrated rats, as expected, exhibited a high water intake (7.36 +/- 0.39 ml/100 g body weight). Central administration of zinc blocked this response (2.5 +/- 0.77 ml/100 g body weight). Naloxone pretreatment (82.5 nmol/rat, 30 min before zinc administration) reverted the water intake to the high levels observed in zinc-free dehydrated animals (7.04 +/- 0.56 ml/100 g body weight). These data indicate that zinc is able to block water intake induced by central ss-adrenergic stimulation and that zinc-induced blockade of water intake in dehydrated rats may be, at least in part, due to stimulation of central opioid peptides.
Highlights
We used adult Wistar male rats weighing 190-250 g kept under controlled light and temperature conditions
We investigated the influence of opiates on zinc-induced inhibition of drinking behavior in dehydrated animals
We have already demonstrated that zinc inhibits water intake in dehydrated rats as well as in rats whose drinking is evoked by central cholinergic and angiotensinergic stimulation [3]
Summary
We used adult Wistar male rats weighing 190-250 g kept under controlled light and temperature conditions (lights on from 6:00 to 20:00 h). To investigate the effect of zinc on ISOinduced water intake, normohydrated animals were treated with third ventricle injection of ISO (160 nmol), after pretreatment (45 min before) with different doses (0.3, 3.0, 30.0 and 300.0 pmol/rat) of Zn(Ac)2 or with NaAc at the dose of 3.0 nmol/rat (controls). Animals were dehydrated (14 h overnight just before the experimental session) and were pretreated with naloxone (10.3 and 82.5 nmol/rat) or saline (controls) 30 min before receiving third ventricle injection of Zn(Ac)2 at the dose of 3.0 pmol/rat.
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