| Abstract: | At low doses angiotensin III (A III) stimulates jejunal fluid absorption in the pentobarbital sodium-anesthetized rat. In contrast, at high doses the hormone inhibits absorption and/or stimulates secretory processes. The stimulation of jejunal absorption in response to A III can be blocked by guanethidine, phentolamine, and prazosin but not by propranolol or yohimbine, suggesting that A III-increased intestinal absorption is secondary to the release of norepinephrine from sympathetic nerves in the jejunum and activation of postsynaptic alpha 1-adrenergic receptors. The A III inhibition of water absorption is not affected by adrenergic antagonists but can be reversed to a net stimulation of transfer after pretreatment of the animals with indomethacin. This suggests that at high doses A III stimulates intestinal prostaglandin biosynthesis. The A III analogue Ile7]A III is devoid of agonist activity over a wide dose range and behaves as a potent antagonist of both the stimulatory and the inhibitory effects of the parent peptide on jejunal absorption. Ile7]A III will be a useful tool for investigating the physiological role of angiotensin peptides in the control of intestinal absorption. |
