Chronic levonorgestrel treatment in Macaca sylvanus: effects on perineal swelling size and fecal sex steroid excretion.

OBJECTIVE: Administered levonorgestrel enables contraception under normal cyclicity of the ovaries and does not suppress the development of cyclic perineal swellings. This study investigated the influence of levonorgestrel on fecal gonadal steroid excretion rates and the expression of perineal swelling size.

SETTINGS: Two groups of Barbary macaque females were observed: Twenty-four implanted individuals under semifree conditions and five non-implanted individuals under caged conditions. Eight of the implanted females had large expressions of the perinea and sixteen reduced. The non-implanted group had no perineal swellings.

METHODS: To determine the individual steroid excretion rates and exzymeimmunoassay for decal samples was established.

RESULTS: Estradiol excretion rates did not differ in distinctively swollen implanted females, but were increased when compared to non-implanted individuals (df=2; p=0.0002). Implanted females with large perineal swellings had lower progesterone concentrations in the feces compared to individuals with reduced swellings and did not differ from the non-swollen group (df=2; p=0.054). Females with large perineal swellings showed a higher calculated estradiol to progesterone ratio index than the other groups (df=2; p=0.0005). Non-implanted individuals showed increased testosterone excretion rates (df.=2; p=0.0001).

MAIN FINDINGS: The results indicate a positive relationship between the perineal swelling size and levonorgestrel implantation.

CONCLUSION: The ratio of fecal estradiol and progesterone titers can be judged as an endocrine indicator for the expression rate of perineal swelling size.