Effects of anandamide on gestation in pregnant rats.

The present study was to test whether the recently described endogenous ligand for the cannabinoid receptor; arachidonyl-ethanolamide (anandamide, ANA), may produce similar effects on pregnancy as the main psychoactive component of marihuana: delta9-tetrahydrocannabinol (THC) in rats. ANA, THC (0.02 mg/kg i.p./day, respectively) or vehicle were injected daily over the third week of pregnancy. The pregnant rats were either killed on day 21 of pregnancy or followed up to delivery. Results show a significant increase in the duration of pregnancy after both THC and ANA treatment. Both drugs caused an increase in the frequency of stillbirths. The mothers' hormone contents in tissues and sera were measured. Decreased LH content was observed in the serum of treated animals. No changes in FSH content were observed either in the pituitary or in the sera. Pituitary prolactin (PRL) levels was lower in ANA treated animals as compared both to controls or THC treated subjects. The serum PRL content decreased in all experimental groups. Decrease in serum progesterone was more prominent in treated rats. Serum levels of prostaglandins (PGF 1alpha and PGF 2alpha) were significantly decreased after THC and ANA treatment. We conclude that ANA has the same tendency to change reproductory parameters in pregnant rats as THC, although in some cases the effects of ANA were slightly different from that of THC. Both endogenous and exogenous cannabinoids inhibit PG synthesis in pregnant rats and this maybe responsible for the delay constitute the mechanism in the onset of labour.