Biological activity of the seminal plasma of alpacas, stimulus for the production of LH by pituitary cells

South American camelids are induced ovulators and require a stimulus to tri gger the LH surge responsible for the ovulation. Seminal plasma (SP) of fer tile alpacas (Lama paces) was tested using a bioassay of pituitary cells to study the effect of seminal plasma on LH release. Plates containing rat pi tuitary cells (2 x 10(5) cells/90-95% viability) were cultured adding: (A) whole SP (WSP) treated with charcoal-dextran, or 1:2 or 1:4 proportions dil uted in culture medium (DMEM/HEPES + antibiotics), or (B) 1:2 SP + anti-GnR H rabbit serum (inhibitory potency 10 (-5) M), or (C) 1:2 SP + anti-GnRH 100 nM synthetic GnRH (buserelin acetate) or (D) 100 nM, 50 nM, 10 nM, and 1 nM synthetic GnRH. Concentration (ng/ml) of LH secreted (Sec) and contain ed (Con) was analyzed using RIA I-125 and the percentage of Sec and Con in each experiment was determined. The results of LH Sec for the cells treated with 50, 10, and 1 nM GnRH were 39, 13, and 1.5%, respectively (r(2) = 98. 41%, r = 0.9920) but cells treated with 100 nM GnRH secreted 10% of LH. Wit h WSP, 1:2, or 1:4 SP the LH Sec was of 44.5% (3.25 ng/ml), 27% (1.9 ng/ml) , and 18% (1.2 ng/ml), respectively. The exposure of cells to 1:2 SP + anti -GnRH, or to 1:2 SP + anti-GnRH/100 nM GnRH produced 31% (2.20 ng/ml) and 3 0% (1.8 ng/ml) of LH Sec, respectively. These results suggest that the SP o f alpacas could have some factor(s) different from GnRH that would contribu te to the mechanisms of LH secretion and to the induced ovulation in the fe male alpaca. (C) 1999 Elsevier Science B.V. All rights reserved.