Discrepancies in the response of the insulin secreting cells of the dog and rat to different adrenergic stimulating agents

Abstract

Our experiments were carried outin vitro on different isolated and perfused pancreas preparations: adult rat pancreas, newborn dog pancreas, uncinate process and splenic portion of adult dog pancreas. The perfusion liquid contained 1.5 g/l glucose. 1) L-isoprenaline (0.05 µM), a stimulating agent of the β-adrenergic receptors, provoked only a slight and brief stimulation of insulin secretion from the rat pancreas. At the same concentration, this substance provoked a considerable stimulation of the insulin secreting cell of the newborn dog pancreas and a still much more marked response from the uncinate process and the splenic portion of adult dog pancreas. The effects of salbutamol (0.09 µM), a stimulating agent of the β-adrenergic receptors, were comparable to those of isoprenaline. The effects of isoprenaline and salbutamol on these preparations were suppressed by propranolol. 2) As to the effects of L-adrenaline on these different preparations, the following results have been recorded: a) Adrenaline (0.011 µM) inhibited insulin secretion by rat pancreas; this effect was suppressed by phenoxybenzamine; it was not modified by propranolol. — b) Adrenaline (0.011 µM) exerted an inhibitory effect on newborn dog pancreas, but only temporarily. Phenoxybenzamine inversed the effects of adrenaline and allowed the appearance of stimulation of insulin secretion; propranolol accentuated the inhibitory effect of adrenaline. — c) On the uncinate process of the adult dog pancreas adrenaline (0.011 µM) provoked a biphasic effect: brief and strong rise of insulin secretion followed by slight inhibition. Phenoxybenzamine enhanced the adrenaline-induced stimulation and transformed the inhibition of the second phase into strong stimulation. Propranolol suppressed the stimulatory effect of adrenaline which then had only an immediate and strong inhibitory effect. Adrenaline at 0.055 µM concentration provoked an extremely brief hypersecretion peak which was less intense than that recorded when using the 5-times weaker concentration; this peak was followed by strong and lasting inhibition.