Plasma progesterone concentrations in the female Natal clinging bat (Miniopterus schreibersii natalensis).

Plasma progesterone concentrations measured by radioimmunoassay in the Natal clinging bat remained below 2.01 ng/ml during lactational anoestrus but increased significantly during the period of delayed implantation. Values peaked at implantation but were followed by a significant decrease thereafter. Concentrations remained low (less than 6.0 ng/ml) during the initial period of fetal development (153-180 days post coitum) and attained peak values (85.6-181.3 ng/ml) 216-222 days after fertilization. The marked post-implantation increase in progesterone concentrations coincided with a significant increase in placental weight.