A RADIOIMMUNOASSAY FOR AFRICAN CATFISH GROWTH-HORMONE - VALIDATION AND EFFECTS OF SUBSTANCES MODULATING THE RELEASE OF GROWTH-HORMONE

A highly sensitive radioimmunoassay has been developed for measuring p lasma growth hormone (GH) concentrations in the African catfish (Clari as gariepinus). The lower detection limit of the assay was 0.1 ng/ml a nd the standard curve had an ED(50) value of 0.5 ng/ml. The validity o f the assay was established and the effects of several neurotransmitte rs on the release of GK were examined. In vitro experiments, using a s tatic culture system for dispersed pituitary cells, demonstrated that the GH release in African catfish was affected by growth hormone-relea sing hormone and somatostatin. Single intraperitoneal injections with a dopamine agonist, apomorphine, produced significant and dose-depende nt increases in plasma GH levels. Unlike carp, goldfish, and tilapia, a super-active analogue of salmon gonadotrophin-releasing hormone did not alter plasma GH levels in African catfish. (C) 1996 Academic Press , Inc.