Absorption of bioactive human growth hormone after oral administration in the common carp (Cyprinus carpio) and its enhancement by deoxycholate

Abstract

Recombinant human growth hormone was administered orally to carp and serum levels of absorbed bioactive hormone were investigated using a highly sensitive Nb2 rat lymphoma cell bioassay and radioimmunoassay. Serum levels of bioactive hGH reached maximum values 30 min after oral intubation and then gradually decreased. Co-administration of the hormone with deoxycholate to fasted carp resulted in up to a 1000-fold increase in absorption compared to aqueous solutions of the hormone, but had no effect on the kinetics of the absorption process. Absorption of the hormone in starved fish was significantly greater than in fed fish. A linear dose-response relationship was observed for hGH in starved fish and the level of absorption in fed fish was influenced by the time interval from the last meal. The ratio of bioactive to immunoactive hGH in fasted fish indicated little loss of bioactivity and also that deoxycholate may be protective against hGH degradation. The present study demonstrates for the first time that biologically active hGH is absorbed in the common carp after oral intubation. Furthermore, the use of a biological detergent dramatically increased the extent of hGH absorption. Additional studies are required to establish the appropriate conditions (diet composition, feeding level, and frequency, etc.) in which polypeptide hormones could be introduced orally to fish.