IN-VIVO AND IN-VITRO EFFECTS OF HUMAN GROWTH-HORMONE ON RAT INTESTINAL ION-TRANSPORT

It has been reported that: 1) ovine growth hormone stimulates intestin al water, sodium, and chloride absorption and 2) specific growth hormo ne receptors are present in the rat intestine. Aims of this work were to investigate the effects of acute administration of hGH on water and ion transport in the rat ileum in vivo and in vitro. In vivo, the abs orption rates of water, sodium, chloride, and potassium were determine d in the rat perfused ileum, during a basal period and after i.v. admi nistration of 6 mug/kg recombinant DNA-derived hGH. In vitro, electric al parameters were measured before and after the hormone addition to t he mucosal or the serosal side of rat ileal mucosa mounted in Ussing c hambers. In vivo, growth hormone induced a rapid increase in the absor ption rates of water, sodium, chloride, and potassium. In vitro, the s erosal, but not the mucosal, addition of growth hormone induced a rapi d decrease of transepithelial potential difference and of short-circui t current. The effect was time- and dose-dependent, saturable, but not reversible in the short time. The electrical effect was abolished in the absence of chloride, indicating that it was related, at least in p art, to inhibition of basal active chloride secretion. Growth hormone also reduced the short-circuit current increase induced by the secreta gogues Escherichia coil heat-stable enterotoxin, theophylline, and cal cium ionophore A23187. These results indicate that hGH has a rapid abs orptive effect that is related, at least in part, to a direct intestin al antisecretory mechanism. It also reduces active intestinal secretio n induced by various secretagogues.