Levels of pro-neo-endorphin/dynorphin-derived peptides in the hypothalamo-posterior pituitary system of male and female Brattleboro rats

Abstract

Immunoreactivities for leucine-enkephalin and the related opioid peptides α-Neo-endorphin, dynorphin(1–17) and dynorphin(1–) were measured in hypothalamus and poterior-intermediate pituitary extracts from male and female Brattleboro rats homozygous (unable to produce vasopressin) and heterozygous(able to produce vasopressin) for daibetes insipidus. In hypothalamus no differences were found in peptide levels among the 4 groups of animals. In contrast, striking, but variable differences were found in posterior intermediate pituitary. In homozygous male animals dynorphin(1–17) immunoreactivity was not significantly different from levels measured in heterozygous male animals. Immunoreactivities for the 3 other peptides, however, showed greatly reduced levels in homozygous male animals compared to heterozygous male animals. Female homozygous animals had greatly reduced levels of all 4 peptides (including dynorphin(1–17) compared to female heterozygous controls. In addition, female heterozygous animals had considerably higher levels of all peptides than male heterozygous animals. In contrast, no sex differences were found in normal Long-Evans rats of the strain from which Brattleboro rats were derived. The following conclusions could be drawn from these findings. (1) Homozygous Brattleboro rats have reduced levels of Leuenkephalin-related opioid peptides in posterior pituitary due to defect or alteration of secretion or turnover but dot due to a defect in biosynthesis. (2) This defect is partially sex dependent and is directly or indirectly linked to the vasopressin deficiency. (3) Since normal rats do not show sex differences in peptides levels, the partial sex dependence of the opioid peptide defect in posterior pituitary seems to be X-chromosomally linked to the vasopressin deficiency.