Comparison of the developmental patterns of vasopressin, glucagon and α-adrenergic receptors from rat-liver membranes

Abstract

The ontogenic developmental patterns of vasopressin, glucagon and α-adrenergic receptors in liver were studied by using membrane fractions prepared from rats aged from 19 days postcoitum to 29 days post-partum. Tritiated lysine-vasopressin ([ 3H] vasopressin), iodinated glucagon ([ 125I]glucagon) and tritiated dihydroergocryptine ([ 3H]DHEC) were used as specific labelled ligands of these receptors. Vasopressin, glucagon and α-adrenergic receptors detected on liver membranes from foetuses or young rats had characteristics identical with those found on liver membranes from adult animals as regards apparent dissociation constants for their respective specific ligands. Furthermore, vasopressin liver receptors from young animals discriminated as efficiently as liver receptors from adult rats between the 3 natural neurohypophyseal peptides: lysine-vasopressin, arginine-vasopressin and oxytocin. Liver α-adrenergic receptors from young and adult rats were mainly of the α 1 type as judged by their high affinity for prazosin and much lower affinity for yohimbine. Membrane contents in vasopressin, glucagon and α-adrenergic receptors expressed in terms of pmoles per mg membrane protein exhibited marked variations during ontogenic development. The respective developmental patterns for the 3 receptors studied were different. Thus, vasopressin receptors were undetectable in liver membranes from foetuses and only few at birth. Membrane content in vasopressin receptors rose rapidly up to the adult level between the 6th and 21st days after birth. The number of glucagon receptors measured in the youngest foetuses tested (19 days) represented about 15% of that determined in adult rats; it rose progressively to reach 75% of the adult rat level in the 29-day-old animals. The evolutionary pattern of α-adrenergic receptors was biphasic. The number of receptors found in 19-day-old foetuses was about 1.5 times the number observed in adult rats; during the later foetal period and the first 2 weeks after birth, this number dropped to about one quarter and then rose to reach the adult level at the end of the weaning period. For vasopressin receptors, a close resemblance was noted between the pattern observed in the liver and that previously described for the rat kidney.