Development and validation of a simple, sensitive enzyme immunoassay (EIA) for quantification of prolactin in buffalo plasma

A simple and highly sensitive enzyme immunoassay (EIA) was developed and validated for prolactin quantification in buffalo plasma (on a microtitreplate) using the biotin–streptavidin–peroxidase amplification and immobilized antiserum in a competitive assay. Prolactin standards (range: 5–5000 pg/(well 50 μL)) were prepared in hormone-free plasma collected from minimal stress non-lactating buffalo heifers in temperate weather. The sensitivity of the EIA procedure was 5 pg/(well 50 μL) (corresponds to 0.1 ng/mL plasma); the 50% relative binding sensitivity occurred at 160 ng/(well 50 μL). Plasma volumes for the EIA, viz. 12.5, 25, and 50 μL, did not influence the shape of standard curve. A parallelism test was carried out to compare the endogenous buffalo plasma prolactin with bovine prolactin standard. To validate the assay biologically, 11 Murrah buffaloes were given a third-generation antiprolactin (Norprolac; 10 mg/animal, i.m.). Blood samples were collected 1 d prior to the start of Norprolac administration and continued up to seventh day in an Ovsynch treatment program. In all animals, there were abrupt declines in prolactin concentrations following Norprolac treatments, which confirmed the biological validation of the EIA. After development and validation of EIA procedure, the concentration of plasma prolactin was determined efficiently in samples collected during both summer and winter samples.