On the relative biological and immunoreactive potencies of luteinizing hormone in the oestradiol benzoate-treated male rat.

Mature male Sprague-Dawley rats were treated with 50 microgram oestradiol benzoate (OeB) per day for 7 days and killed 24 h after the last injection. Serum and pituitary luteinzing hormone (LH) levels were measured by RIA using NIAMDD rat hormone for iodination code I4 (rLH-I4) combined with either NIAMDD-anti-rat LH serum 3 (AS3) or serum 1 (AS1). Pituitary LH levels were also measured by an in vitro bioassay procedure in which testosterone production by dispersed rat testicular interstitial cells is related to the concentration of LH. Pituitary LH levels were reduced in OeB-treated rats regardless of which of the three assay systems was used. However, absolute values obtained in all three assays systems were statistically correlated. OeB-treatment did not significantly alter the relative bioassayable and immunoassayable potencies of LH present in pituitaries at autopsy. OeB-treated rats had non-detectable serum LH levels as measured by RIA using either AS1 or AS3 in combination with [125I]rLH-I4. These results confirm that chronic OeB-treatment decreases pituitary LH and suggest a decrease in serum LH as well. Comparison of the present with previous results revealed particular combinations of RIA reagents yield divergent estimates for serum LH in OeB-treated male rats. This situation emphasizes the need to carefully specify all RIA reagents used in any study since the results may very with different lots of RIA regents.