Vasopressin increases the ovulatory response to PMSG in immature rats (de la Lastra & Forcelledo, 1970). This effect of vasopressin on ovulation, as well as the similarity between the three terminal amino acids of arginine-vasopressin (AVP) and LH-FSH releasing hormone (LH-FSH-RH), induced us to study the influence of the peptide, Pro-Arg-Gly-NH2 (PAGA), which is the terminal fragment of AVP, on the ovulation induced in adult rats with LH or LH-FSH-RH.
Both LH-FSH-RH and PAGA were synthesized by the solid-phase method, using standard techniques (Stewart & Young, 1969). The normal chloromethylated 1% cross-linked polystyrene was used as support, and α-amino groups were blocked with the tert-butyloxycarbonyl group. Toluenesulphonyl blocking groups were used for histidine- and arginine-side