Effect of oxytocin and PGF2 alpha on prolactin release in sows.

Experimental sows were divided into three groups treated as follows: Group I (n = 3): on Day 12 of the oestrous cycle i.m. injection of oxytocin (OT) at a dose of 0.25 I.U./kg b.w.; Group II (n = 4): on Day 12 and 13 of the oestrous cycle i.v. injections of OT (0.03 I.U./kg b.w.), and Group III (n = 3): on Day 13 of the oestrous cycle i.m. injection of cloprostenol (prostaglandin F2 alpha analogue; PG) at a dose of 500 micrograms. Blood samples were collected from the jugular vein for 2 h before and 2 h or 4 h after OT and PG treatment, respectively. Concentration of prolactin (PRL) was determined in all studied groups, whereas 13,14-dihydro-15-keto-PGF2 alpha (PGFM) was estimated in Group I and II. OT injections (i.v. or i.m.) Day 12 and 13 of the oestrous cycle raised its concentrations in the peripheral blood lasting for 50 and 120 min, respectively. But short lasting rise of PRL was caused by OT in 3 sows, whereas of PGFM in 2 sows only. In all other studied sows values of PRL and PGFM were during an experiment on the pre-treatment level. However, if PGF2 alpha analogue was injected on Day 13 of the cycle, it caused significant rise of PRL concentration (P less than 0.01) 20 min after treatment. PRL concentration measured after PG administration (7.0 +/- 0.7 ng/ml) was statistically higher (P less than 0.01) compared to the period proceeding PG injection (2.6 +/- 0.3 ng/ml).(ABSTRACT TRUNCATED AT 250 WORDS)