Dietary hormonal modification of growth, intestinal ATPase, and glucose transport in tilapia

The effect of growth stimulatory and inhibitory dietary applications of hormones [3,5,3'-triiodo-L-thyronine (T3) and 17 alpha-methyltestosterone (MT)] on Na+-K+-adenosinetriphosphatase (ATPase) activity and glucose transport by upper and lower intestinal brush-border membrane vesicles of tilapia (Oreochromis mossambicus) were characterized. Both enzyme activity and glucose transport were greater in growth-stimulatory treatments and lower in growth-inhibitory treatments than in the control. Growth on stimulatory hormone treatments increased apparent glucose influx kinetics (one-half maximum glucose influx, maximum glucose influx, and apparent diffusion coefficient) in both intestinal segments, whereas inhibitory treatments reduced these parameters in upper intestine but had no effect on these parameters in lower intestine. All hormone treatments increased the stoichiometry of Na-glucose cotransport from 1:1 in the control to 2:1 under test conditions. It is suggested that observed patterns of altered growth are due, in part, to hormonally modified intestinal nutrient transport and Na+-K+-ATPase activities.