DEVELOPMENT OF A SPECIFIC RADIOIMMUNOASSAY FOR NEUROPEPTIDE-K - ITS APPLICATION TO SIBERIAN HAMSTER TISSUES

In this report we describe the development of a radioimmunoassay for n europeptide K (NPK) that, is not influenced by the presence of free ne urokinin A (NKA) or neuropeptide gamma (NPG). The antisera for the rad ioimmunoassay were obtained by immunizing rabbits with beta-preprotach ykinin A fragment 69-91. This fragment contains the sequence 1-20 of N PK and has only the sequence 18-20 (Gly-His-Gly) in common with NPG. T wo antisera were obtained, neither cross-reacting with NKA or NPG. The specificity of these antisera was confirmed by the finding of a major immunoreactive peak in the eluates obtained from HPLC separation, cor responding to NPK. This radioimmunoassay was applied to the determinat ion of NPK in hypothalamic and anterior pituitary extracts from Siberi an hamsters. Hypothalami from male and female hamsters contained simil ar concentrations of NPK, although slightly higher in males. NPK level s in the hypothalamus of female Siberian hamsters showed few fluctuati ons during the estrous cycle, with the levels measured at estrus being significantly lower than at proestrus, diestrus I, and diestrus II. I n anterior pituitaries from Siberian hamsters the concentrations of NP K were significantly lower in females than in males. This radioimmunoa ssay has demonstrated the presence of NPK in the anterior pituitary gl and of the Siberian hamster, and it should be very useful for future s tudies on mechanisms of regulation of NPK secretion in different tissu es.