Postpartum infertility in common chimpanzees

The endocrine profile during normal postpartum amenorrhea in chimpanzees (Pan troglodytes) closely resembles that of women, and its duration is similarly extended by nursing. However, when infant chimpanzees in our colony were removed at birth, excessively prolonged postpartum amenorrhea (7-26 months duration) occurred in 24% of cases. Our endocrine studies indicate that such prolonged postpartum amenorrhea (PPAm) is a pathological condition associated with chronically elevated serum prolactin levels and galactorrhea. In the absence of nursing, we sought an alternate behavioral basis for PPAm. Breast and genital auto- and partner-directed manipulation was compared in PPAm chimpanzees, normal 2-3 mo. postpartum chimpanzees (infants removed at birth), and regularly-menstruating chimpanzees. A statistically significant pattern of breast, but not genital, manipulation was observed in the PPAm group only, at levels comparable to normal suckling. In particular, a characteristic pattern of nipple auto-manipulation (spooling) occurred. Two partner-stimulated PPAm animals were also identified: when caged individually, they resumed cycling within a few days. In contrast, 2 self-stimulators did not resume cyclicity when isolated. These observations suggested that interruption of breast stimulation allowed cyclicity to resume. Treatment of PPAm chimpanzees with oral Bromocryptine Mesylate (Sandoz, 2.5-5.0 mg b.i.d.) was associated with depression of prolactin levels in most animals and resumption of cyclicity in 11/13 subjects within 4 months. Oral Pergolide (Eli Lilly, 200 μg once daily, 13-17 days), appeared much more effective, cyclicity resumed in 8/8 animals within 14 days of commencing treatment; both drugs significantly reduced postpartum amenorrhea duration.