Functional characterization of luteinizing hormone responsiveness and desensitization in perifused interstitial cells

The characteristics of the steroidogenic response of isolated rat testis interstitial cells to repeated 10 min pulses of ovine LH at 2 h intervals were examined in a Bio-gel perifusion system. Maximal responsiveness of the perifused interstitial cells could be maintained for 6-8 h. Thereafter, both basal and LH-stimulated testosterone production declined gradually despite supplementation of the perifusion medium with 1% and 5% foetal calf serum or 0.5 microgram/ml insulin. In contrast to the time-related steroidogenic decline, a dose-dependent refractoriness of the interstitial cells could be induced by repeated exposure to LH pulses from 0.01 to 10 ng/ml during the first 6 h of perifusion. The higher the stimulating dose of LH, the greater was the rate and magnitude of the resultant desensitization. With lower doses (0.01 and 0.1 ng/ml) of LH, an initial sensitization or priming effect was also observed. These changes in steroidogenic response occurred in the absence of any significant alterations in LH/hCG receptor binding of the perifused interstitial cells, nor could the refractory state be overcome by stimulation with analogues of cAMP. The perifused interstitial cells, when desensitized with low doses of LH (0.1 ng/ml), were capable of increasing or maintaining testosterone production in response to further stimulation with higher doses of LH (1 and 10 ng/ml). The mechanism(s) underlying the in vitro desensitization of perifused interstitial cells by LH may best be explained on the basis of the interaction between the negative effects of substrate depletion and the positive influence of mobilization of substrate(s) into the metabolically active pool for cholesterol side-chain cleavage. It was concluded that the dose of LH used in the pulsatile stimulation of perifused interstitial cells is critically important not only in determining the total amount of testosterone produced, but also in the pattern of response in terms of the degree of sensitization and desensitization induced.