Biphasic action of growth hormone on intestinal amino acid absorption in striped bass hybrids

1. 1. Weekly injections of bovine growth hormone (bGH) increased the maximal transport rate of both Na⁺-dependent and Na⁺ -independent l-leucine transport with little effect on the affinity constants in the intestine of striped bass hybrids. 2. 2. The Na⁺-dependent and the Na⁺-independent transport of the non-metabolizable analog cycloleucine was also stimulated by bGH. 3. 3. The Na⁺ -dependent active transport was stimulated 2 days after the hormone treatment, while the stimulation of the Na⁺-independent diffusional transport was not observed until after 2 weeks of treatment. 4. 4. Studies of intestinal morphometry and l-leucine transport using brush border membrane vesicles suggested that bGH affects intestinal amino acid absorption initially by increasing the number of transporters per cell. 5. 5. This phase is followed by a general increase of the intestinal mass after long-term treatment with the hormone.