Parenteral administration of progestin Nestorone® to lactating cynomolgus monkeys: An ideal hormonal contraceptive at lactation? (PDF)
Heikinheimo,Oskari; Ranta,Sirpa; Moo-Young,Alfred J.; Lahteenmaki,Pekka; Gordon,K.
Human Reproduction 14(8): 1993-1997
Publication date: 1999
Nestorone (NES) progestin is highly effective for contraceptionfollowing parenteral administration, but ineffective after oralingestion due to rapid first-pass metabolism. Thus, NES mightbe ideal for lactational contraception; possible NES in milkshould be metabolized by the nursing infant. We evaluated thedistribution of NES, its endocrine effects and infant weightgain in five cynomolgus monkeys and their nursing infants. Nestoroneimplants, releasing ~40 µg NES/day in vitro, were placeds.c. in the mothers 3-4 months following delivery, wherethey remained in situ for 4 weeks. Sampling (blood daily fromthe mother; milk and blood from the infant at 3 day intervals)was initiated at 2 weeks prior to insertion, and continued for2 weeks following removal of the implant. NES, oestradiol, progesteroneand prolactin were measured by radioimmunoassays and the infantswere weighed weekly. The (mean ± SD) maternal serum andmilk concentrations of NES were 337 ± 90 and 586 ±301 pmol/l during the use of the implants. The ratio of milk/serumNES was 1.68 ± 0.12 (mean ± SE), and the serumand milk concentrations were significantly correlated (r = 0.75,P < 0.001). NES was not detectable (<13 pmol/l) in anyinfant serum samples. Concentrations of prolactin (mean ±SD) were 41.1 ± 32, 26.7 ± 7.6 and 26.3 ±9.5 ng/ml before, during and after the use of the implants respectively.The (mean ± SE) infant weight increased from 643 ±54 g 1 week prior to insertion to 713 ± 54 g 1 week followingremoval. These data confirm that NES in milk is rapidly metabolizedby the suckling infant. Therefore, NES appears to be an idealhormonal contraceptive for use during lactation.