Induction of the acrosome reaction in dog sperm cells is dependent on epididymal maturation: The generation of a functional progesterone receptor is involved

In the current study we investigated the progesterone receptor exposure on the sperm from the testis and different parts of the epididymis, the relati on to the sperm maturation stage, the functionality of the progesterone rec eptor and the capacity of sperm to undergo acrosome reaction. Exposed proge sterone receptors on spermatozoa were detected using Progesterone-BSA conju gate labeled with fluorescein isothiocyanate (P-BSA-FITC) or a monoclonal a ntibody against progesterone receptor, C-262. Either progesterone or calciu m ionophore was used to induce acrosome reaction. A high percentage (69 +/- 8%; mean +/- SD) of sperm atozoa from the cauda epididymis is showed P-BSA -FITC labeling at the onset of incubation, whereas only 0.1 +/- 1 and 4 +/- 2%, of spermatozoa from the testes, caput, and corpus epididymis, respecti vely, were labeled. There was no significant increase in P-BSA-FITC binding during the course of a 6 hr incubation. Treatment with either 10 muM proge sterone or 5 muM calcium ionophore induced acrosome reaction in cauda epidi dymal sperm but not in testicular sperm, caput or corpus epipidymal sperm. It is concluded that the matured sperm of the dog from cauda epididymis and freshly ejaculated sperm demonstrate a functional membrane-bound progester one receptor while less matured spermatozoa from the testicle, caput, and c orpus epididymis fail to demonstrate such a receptor. Acrosome reaction of dog sperm can be induced using either progesterone or calcium ionophore; ho wever, the maturation stages of spermatozoa influence this occurrence. (C) 2001 Wiley-Liss, Inc.