General and Comparative Endocrinology vol:104 issue:2 pages:147-155
A highly sensitive radioimmunoassay has been developed for measuring plasma growth hormone (GH) concentrations in the African catfish (Clarias gariepinus). The lower detection limit of the assay was 0.1 ng/ml and the standard curve had an ED(50) value of 0.5 ng/ml. The validity of the assay was established and the effects of several neurotransmitters on the release of GK were examined. In vitro experiments, using a static culture system for dispersed pituitary cells, demonstrated that the GH release in African catfish was affected by growth hormone-releasing hormone and somatostatin. Single intraperitoneal injections with a dopamine agonist, apomorphine, produced significant and dose-dependent 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.