Further studies on the localization of angiotensin-II-like immunoreactivity in the anterior pituitary gland of the male rat, comparing various antisera to pituitary hormones and their specificity.

Using immunocytochemistry with the sensitive avidin-biotin complex method and an antibody to the beta subunit of rat luteinizing hormone (rat LH beta) provided by the National Hormone and Pituitary Program, NIADDK, to identify gonadotrops, the presence of angiotensin II-like immunoreactivity in the gonadotrops of the anterior pituitary gland of male rats was confirmed. However, using an antibody to rat prolactin, no angiotensin II-like immunoreactivity could be found in lactotrops. This finding is at variance with a previous report from this laboratory, in which the lactotrops were identified with an NIADDK antibody to human prolactin. The possibility that the antibodies to human prolactin cross-reacted with rat LH was therefore investigated by a noncompetitive radioimmunological binding assay. At the same dilution used in immunocytochemistry, two different NIADDK antihuman prolactin antisera displayed 49% and 24% binding of labeled rat LH beta. Similar cross reactions were demonstrated immunocytochemically. There was no cross reactivity between rat LH beta and the antibody to rat prolactin. Consequently, the staining reported to be in lactotrops in the previous study was probably in gonadotrops.