Significantly, IL-1 was clearly detectable even at a very large dilution of the IF (1:1000) in the in vitro bioassay. However, in some experiments the stimulatory activity of IF was not completely blocked by IL-lra even though this is a maximally inhibiting dose. Moreover, there was residual stimulatory activity in at least some IF samples after heating to 100°C, although purified IL-1 is not heat stable. These data suggested that there are additional stimulatory factors in IF that may potentiate the IL-1 response in vitro. Nonetheless, the data indicate that the levels of IL-1 bioactivity in testicular IF are much higher than found in normal serum and are several times higher than the concentration required to exert a biological response. buy asthma inhaler
While there are large numbers of macrophages present in the rat testis, these cells are not stimulated, and unstimulated macrophages do not secrete IL-1. In fact, the resident testicular macrophages have a very poor capacity for secretion of IL-1, even in response to stimulation. There is evidence that IL-ip circulates at low levels even in normal serum, and circulating IL-1 has access to the testicular interstitium, but this would not account for the very high levels observed in the testis in the present study. Consequently, the most likely source for the bioactive IL-1 in testicular IF is the Sertoli cells, which secrete IL-la in vitro. Recent mRNA data have also implicated the meiotic germ cells as a potential source. There is considerable evidence that IL-1 is involved in regulating spermatogenesis, and spermatogonial proliferation in particular. Although primarily intracellular or membrane bound, soluble IL-la has been found in several other biological fluids in vivo.