Carnitine and Glycerylphosphorylcholine in the Reproductive Tract of the Male Rat

Abstract

Carnitine and glycerylphosphorylcholine (GPC) levels have been measured in the reproductive tissues of male rats, with special reference to the epididymis. The increase in concentration of these compounds in reproductive tissues during the prepubertal and pubertal periods has been examined and their distribution along the epididymis has been determined in mature animals. Carnitine accumulates in the epididymal plasma in the cauda epididymidis whilst GPC accumulates in the caput epididymidis. By developing a new technique for the collection and separation of epididymal spermatozoa and undiluted fluid from the cauda epididymidis, the concentrations of carnitine, acetylcarnitine and GPC have been measured and the free fatty acid composition of epididymal plasma has also been determined and compared with blood plasma. By examining the effects of castration, testosterone replacement and cryptorchidism, the accumulation of carnitine and GPC in the epididymis has been shown to be under androgen control. By contrast, the anti-androgens, cyproterone acetate and medroxyprogesterone acetate, did not influence secretory activity, perhaps because their effect was nullified by a high androgen concentration in epididymal plasma. The antifertility compound \ g=a\ \ x=r eq-\ chlorohydrin was also shown to be without effect on the concentration of carnitine and GPC in the reproductive tract. The relationship of carnitine and GPC to the metabolism of fatty acids by spermatozoa is discussed.

The distribution of carnitine and acetylcarnitine in the epididymis and epididymal spermatozoa of the boar

“…The acetylcarnitine amount was very low whatever the region of the epididymis considered. The carnitine acylation state of the epididymal fluid from other species (Casillas & Chaipayungpan, 1979;Casillas et al, 1984;Brooks et al, 1974) is greater than that reported here. However, only the acetylcarnitine was estimated in our study, and the fluid sampling technique used prevented all leakage from epithelial cells.…”

“…Carnitine accumulates in spermatozoa as they mature in the epididymis as shown in the rat, bull, monkey, boar (Casillas, 1972(Casillas, ,1973, rabbit (Casillas & Chaipayungpan, 1979), ram (Inskeep & Hammerstedt, 1982) and hamster (Casillas et al, 1984). In-vitro studies have revealed that carnitine is rapidly acetylated when bovine epididymal spermatozoa are incubated with physiological substrates (Casillas & Erickson, 1975), whereas long-chain acylcarnitine is not detectable (Casillas, 1973;Brooks et al, 1974;Van Dop et al, 1977). In vitro, acetylcarnitine serves as a readily accessible energy store which can be used when there is a great demand for energy in bovine epididymal spermatozoa (Milkowski et al, 1976).…”

Carnitine content of rabbit epididymal spermatozoa in organ culture

“…Carnitine is present in exceedingly high concentration in the epididymis of rats (Marquis & Fritz, 1965a;Casillas, 1972;Brooks, Hamilton & Mallek, 1974) and other species (Casillas, 1972). Carnitine accumulates in bovine (Casillas, 1973) and in rabbit (Casillas & Chaipayungpan, 1979) spermatozoa as they mature in the epididymis and we have suggested that one of the functions of the organ is to supply carnitine to spermatozoa as they mature.…”

The interaction of -chlorohydrin with glycerol kinase

“…Moreover, high concentrations of glycerol can overcome the inhibitory effect of a-chlorohydrin on ram spermatozoa (Edwards et al, 1976;Brown-Woodman et al, 1978), suggesting competition between the two compounds for the same pathway. Such competition is supported by the report that a-chlorohydrin is a competitive inhibitor of glycerol kinase prepared from Escherichia coli (Thorner, 1972; see Brooks, Hamilton & Mallek, 1974 (Blackshaw, 1954) and the spermatozoa were separated from seminal plasma by the procedure of Harrison (1976). The pellet of spermatozoa was frozen and subsequently thawed and sonicated for a total of 1 min in 50 mM-triethanolamine, 1 iriM-EDTA, 2 mM-MgCl2, 30 mM-mercaptoethanol, 0-75% Triton ¬ 00, pH 7-5.…”

“…The reaction mixture contained 100 mM-4-(2-hydroxyethyl)-l-piperazineethanesulphonic acid, 2 mM-MgCl2, 17-5 mM-ATP, 5 U glycerol kinase/ml, pH 7-0, and no substrate, 50 mM-glycerol or 50 mM-a-chlorohydrin. The Because glycerylphosphorylcholine (GPC) occurs in high concentration in the epididymal plasma (Brooks et al, 1974) and is structurally similar to a-chlorohydrin, this compound was also tested as an inhibitor of glycerol kinase. GPC did cause competitive inhibition of the purified enzyme and the inhibitor constant (54 mM) was of a similar magnitude to that of a-chlorohydrin (30 mM).…”