Histochemistry of 3?-hydroxysteroid dehydrogenase in rat ovary

Abstract

By recording the incubation time needed for initial appearance of the red and blue formazans the reliability of the histochemical method for 3β-HSD was investigated: 1. Prefixation of small tissue blocks with 1% w/v methanol-free formaldehyde (pH=7.2) for up to 30 min preserved morphological integrity as well as maximal enzyme activity. Moreover, the substantivity of formazans and lipids was enhanced. 2. Commercial available glutaraldehyde (pH=7.2) induced SH groups in the tissue (even at 0.1% w/v for 5 min) thereby enhancing the Nothing dehydrogenase reaction. 3. Preextraction of lipids with acetone for 20 min at −30° C caused no loss of activity and was an inevitable step if a reliable activity pattern had to be achieved (e.g. in interstitial cells). 4. No diffusion of enzyme was noticed within 30 min of preincubation in phosphate buffer (0.2 M, pH=7.2) at 20° C. 5. By using the double-section incubation method no diffusion of 3β-HSD or rediffusion of NADH or PMSH could be noticed within 45 min of incubation, provided that low concentrations of NAD (0.1 mg/ml) and PMS (0.003 mg/ml) were balanced against the concentration of Nitro BT (0.5 mg/ml) or Tetranitro BT (1.0 mg/ml). 6. The utility of different inhibitors of alkaline phosphomonoesterase was tested and discussed. 7. By inhibiting alkaline phosphomonoesterase with 0.1 mM ofl-p-bromotetramisole or 16 mM ofβ-glycerophosphate, 3β-HSD was shown to be exclusively NAD-linked. 8. Levamisole was a potent inhibitor of NADH-tetrazolium reductase as well as 3β-HSD, but not of NADPH-tetrazolium reductase. 9. 3β-HSD possess SH groups requisite for the activity as this enzyme was totally inhibited byn-ethyl maleimide. 10. Whether alcohol dehydrogenases may use steroids as substrate is discussed. It is concluded that preextraction (by acetone) and/or the use of an inhibitor of alcohol dehydrogenase (1,10-phenanthroline) has to be performed. 11. Propylene glycol was a poor solvent for all substrates and was itself an excellent substrate for alcohol dehydrogenase. 12. Specifications for the ideal solvent of steroid substrates in the histochemical practice are proposed. DMSO showed to be promising as a steroid solvent (e.g. extraction of formazans was considerably lower as compared to DMF). 13. The utilization of substrates was descending in the following order (using 1 mM and 0.1 ml/ml of either DMF or DMSO): epiandrosterone, methandriol, dehydroepiandrosterone and pregnenolone. 4. If DMSO was used as solvent for pregnenolone (but not for the other substrates tested) an evident increase of activity was recorded as compared to DMF.