Further analysis of the occurrence of pigeon crop sac-stimulating activity (Prolactin) in the vertebrate adenohypophysis

Abstract

Extracts of acetone-dried pituitary glands from representatives of all vertebrate classes were tested for pigeon crop sac-stimulating (PCs) activity using objective, quantitative methods. Extracts of acetone-dried liver and brain tissue combined, or of acetone-dried liver tissue alone, were used to obtain quantitative assessment of nonspecific responses. The crop-sac responses were quantified by removing a standard 4-cm-diameter disc of mucosal epithelium from the site of injection. The dry weight, fat content, and RNA and DNA levels in this disc were determined. Only Tilapia mossambica and Mugil cephalus of eight teleostean species tested gave results which indicated that their “prolactic” had significantly, albeit minimally effective PCs capacity. Responses to other fish pituitaries, including a cyclostome and a chondrichthyean, were not significantly different from those to nonpituitary control tissue. In contrast with the results obtained with the control and fish-pituitary preparations, extracts of the glands of the African lungfish ( Protopterus aethiopicus), and of anurans, urodeles, and a reptile, were as effectively crop sac-stimulating as extracts of pituitaries from homeotherms. The only species in the lungfish-tetrapod group whose pituitaries did not show more effective PCs activity than all of the fish pituitary preparations was the toad, Bufo marinus. However, the Bufo pituitaries were significantly more effective than the glands of six of the eight teleost species. The possibility that fish pituitaries contain factors which inactivate or interfere with the action of teleost “prolactin” on the crop sac was investigated. An extract of combined pigeon and pollack pituitaries was compared with pigeon pituitary extract alone. The combined extract did not prevent the pigeon prolactin from being fully effective. Extracts of pituitaries from pigeons, lungfish, and three teleostean species were tested for PCs activity at three dose levels. The pigeon and lungfish pituitary extracts gave, in part, log dose-response relationships which paralleled that obtained with ovine prolactin. None of the fish pituitary extracts gave log dose-response relationships which had slopes significantly different from zero. It is concluded that the prolactins of vertebrates in the lungfish-tetrapod line are characterized by a high degree of PCS efficacy. Although the prolactins of some teleostean species may have minimal PCS activity, the pituitaries of fishes characteristically showno specific capacity to stimulate the pigeon crop.