Abstract

Prolactin is a peptide hormone that plays a role in various physiological functions and its production is influenced by several factors (thyrotropin-releasing hormone, dopamine, season, meal feeding or physiological state such as lactation). Plasma levels help understand reproductive physiology; but may also be a useful indicator of dopamine production at a central level (connection between the hypothalamus and pituitary gland). In human medicine, when prolactin is measured using sandwich immunometric methodologies in automated analysers, hyperprolactinemia diagnosis may be confounded by the presence of a high molecular mass prolactin/IgG autoantibody complex termed macroprolactin, which does not have biological effects. Macroprolactinaemia has not previously been described in horses. Previously equine prolactin has been measured by radioimmunoassay (RIA) analysis; however, more rapid ELISA assays are now available without the radioactive tracer health and safety considerations. In this study, prolactin was measured in plasma from 20 normal horses and 20 horses with pituitary pars intermedia dysfunction, using a commercial ELISA assay (Biorbyt, UK). Surprisingly, while most showed values below 100 ng/mL, 13 appeared to have extremely high concentrations, well in excess of the upper limit of the standard curve at 1000 ng/mL. There was no significant association of this finding with disease category, breed, sex or age. To determine whether the presence of macroprolactin could be causing these aberrant values, a polyethyleneglycol (PEG) precipitation step was introduced, as previously shown in humans, to remove the macroprolactin while leaving the monomeric form in solution. After the addition of PEG and centrifugation to precipitate out macroprolactin, the supernatant with the unprecipitated prolactin was tested and compared with unprecipitated samples from the same individuals. PEG precipitation resulted in a reduction in prolactin values by more than 99% in those with apparent hyperprolactinaemia (to below 200 ng/mL in all cases except one at 243 ng/mL). In the other samples the values were reduced from 67.4 ± 9.9ng/ml to 10.6 ± 0.7ng/ml (approximately 75% reduction). Although this data is preliminary and more validation work is necessary, these findings are consistent with macroprolactin being detected by the ELISA assay in these individual horses. While it may be possible to validate the ELISA assay for measuring prolactin in equine plasma, a PEG precipitation step is required to remove this interfering substance. Further research is needed to confirm the presence and size characteristics of this macroprolactin complex in equine plasma.

Full Text
Paper version not known

Talk to us

Join us for a 30 min session where you can share your feedback and ask us any queries you have

Schedule a call