Prolactin secretion patterns are species-specific, variable and influenced by multiple factors including circadian and hormonal cues, stress, physiological state and reproductive strategy. In nonpregnant females, circulating prolactin levels are low; however, during the afternoon of proestrus an estradiol-induced prolactin surge coinciding with the preovulatory LH surge has been recorded in many (but not all) species. In mice, there have been conflicting reports relating to the occurrence and timing of this surge. To gain insight into the characteristics of circulating prolactin levels during proestrus we have used repeated tail tip blood sampling in C57BL/6J and Swiss Webster mice to profile prolactin secretion in individual mice. For this study we have measured prolactin levels during diestrus and proestrus using an ultra-sensitive prolactin ELISA. To establish the relationship between circulating prolactin levels and the timing of the LH surge we have simultaneously measured LH levels in the same samples via ELISA. In mice circulating prolactin levels in proestrus do not follow a classical surge pattern but show prolonged elevation which is not tightly linked to the light/dark cycle.

Mouse plasma samples were processed from whole blood samples obtained by the tail tip sampling method. Full description of sampling method used in doi:10.1111/jne.13129 and based on the method described in doi:10.1210/en.2011-0253. Prolactin and LH were measured by ultra-sensitive ELISA. Intra-assay and inter-assay coefficients of variation for both Prolactin and LH were <10% and <15% respectively.

Proestrus measurements of prolactin and LH taken from mice in which an LH surge was not detected when tail tip blood sampling was performed were excluded from analysis (C57BL/6J n=2, Swiss Webster n=3 excluded).