LOCALIZATION OF PROLACTIN IN REPTILIAN PARS DISTALIS

The relationship between the distribution of prolactin and the various cell types in the pars distalis (PD) of two species of lizard, two species of snake and a turtle were examined in order to determine the site of prolactin production in the reptilian pituitary. Prolactin was measured by pigeon crop-sac bioassay, and, in the turtle, by polycrylamide gel (disc) electrophoresis. Pigeon crop-sac stimulating activity (prolactin) was observed in the pituitary of all species examined. In every case, most of the hormone was localized in the rostral half of the PD and in the lizards none was detected in the caudal region. Disc electrophoresis verified this finding in the turtle and also suggested that a presumptive growth hormone is concentrated in the caudal half of the chelonian gland. Thus, it appears likely that the lactotropes are located rostrally and the somatotropes caudally in the reptilian PD. Histological studies of the PD demonstrate two types of acidophils which show a marked regional distribution; a carminophil is restricted almost entirely to the rostral half of the PD and an orangeophil to the caudal half. On the basis of patterns of hormone distribution, it seems likely that the rostral carminophil is the lactotrope, and the caudal orangeophil may be the somatotrope. © 1969.