Neurohypophysial Peptides in the Bovine Hypothalamus:The Relationship of Neurophysin I to Oxytocin, and Neurophysin II to Vasopressin in Supraoptic and Paraventrieular Regions

Previous studies have suggested that oxytocin may have an intragranular association with the posterior pituitary binding protein neurophysin I (NPI), and vasopressin with neurophysin II (NPII) in the ox. We have studied the possible relationship between oxytocin and NPI, and vasopressin and NPII at their presumed sites of synthesis in the bovine hypothalamus. Separate regions of the supraoptic (SON) and paraventrieular (PVN) nuclei from both sides of the hypothalamus and the posterior lobes of the pituitary glands (PL) of 4 steers were homogenized and extracted. The oxytocin and vasopressin content of these homogenates was determined by bioassay. Vasopressin was also measured by radioimmunoassay, as were NPI and NPII. Both hormones and both neurophysins were found in SON, PVN and PL. The concentrations of NPI and oxytocin in SON and PVN were the same. In the PVN the concentrations of oxytocin and vasopressin and those of NPI and NPII were similar. In the SON, however, NPII and vasopressin concentrations were higher than those of oxytocin and NPI. The SON contained 2–3 times as much NPII and vasopressin as did the PVN. A significant correlation between the vasopressin/oxytocin ratio and the NPII/PI ratio was found in the hypothalamic regions. This correlation was not found in PL, however, where the vasopressin/oxytocin ratio was 0.46 and the NPII content was greater than NPI. These data demonstrate a relationship between NPI and oxytocin, and NPII and vasopressin in the bovine hypothalamus and suggest that a specific neurophysin may be synthesized with each neurohypophysial hormone. (Endocrinology95: 931, 1974)