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Time Course of the Effect of Growth Hormone in Vitro on Amino Acid and Monosaccharide Transport and on Protein Synthesis in Diaphragm of Young Normal Rats^*

KERSTIN ALBERTSSON-WIKLAND and OLLE ISAKSSON

Department of Physiology, University of Gbteborg Goteborg, Sweden

Abstract

The in vitro responsiveness of diaphragms from 18-day-old fasted normal rats to bovine growth hormone (bGH) with time was studied by determining the accumulation of a-aminoisobutyric acid (AIB) and 3–0 methylglucose (3-OMG) and by determining the incorporation of phenylalanine into diaphragm proteins. An estimate of the time course of the effect of GH was obtained by adding the different labeled substances to the incubation medium at different time periods after the start of the incubation. bGH (5 µg/ml) stimulated the uptake of AIB and 3-OMG and the incorporation of phenylalanine between 0–60 min after the start of the incubation. This period was then followed by a period of 60–120 min during which no further stimulation occurred in spite of the continuous presence of the hormone, i.e. the diaphragm was "refractory" to GH. When the incubation period was extended beyond the "refractory phase," the uptake of AIB and the incorporation of phenylalanine once again increased in diaphragms exposed to bGH. The present experiments thus demonstrate that the membrane transport system (s) and protein synthesis in diaphragms of 18-day-old fasted rats pass through a sequence of changes in the response to GH. The fact that GH exerts a biphasic action on membrane transport and protein synthesis in diaphragm muscle of normal rats suggests that this responsiveness pattern to GH with time is a generalized cellular phenomenon in response to the hormone. (Endocrinology 102: 1445, 1978)

Footnotes

^* This work was supported by grants from the S.wedish Medical Research Council (B77-14X-04250–04); Nordisk Insulinfond, Gentofte, Denmark; Magnus Bervalls Stiftelse; Svenska Diabetesforbundet, Stockholm; and the Medical Faculty, University of Goteborg.

To whom requests for reprints should be addressed: Department of Physiology, Fack, S-400 33 Goteborg 33, Sweden.

Received June 6, 1977.