Spontaneous contractions were reduced, while basic responses to oxytocin or PGF2α did not change, suggesting that obesity may reduce uterine contractions (due to the high progesterone and leptin and low proinflammatory cytokine levels) but does not influence the stimulability of the last-day pregnant rat uterus. Here, OXT is linked to obesity due to melanocortin 4 receptor deficiency.