Reduced level of uterine norepinephrine transmitter during hCG-induced pseudopregnancy in the rabbit.

The bulk of rabbit uterine norepinephrine is present in short adrenergic neurons which have unique functional properties. Pseudopregnancy was induced in adult nulliparous rabbits by a single injection of 1,500 IU of human chorionic gonadotrophin (hCG). By the 6th day of pseudopregnancy, the total uterine content of norepinephrine was reduced to a level only 40% of that found in untreated controls. At 12 days after the injection the amine level was greater than at 6 days but still significantly less than in controls. By 18 days, when the progestational proliferation of the endometrium had subsided, the levels in uteri of control and injected animals were similar. The findings support previous findings indicating the presence of a peripheral neuro-endocrine mechanism influencing uterine motor function.