N OCIETY' - the Society for Reproductive Biology

MICROARRAYS: MICRO OR MACRO POTENTIAL?The Effect of Cyclic-Nucleotides on Fluid Reabsorptionin the Ductuli Efferentes Testis of the Rat.Suet Y. Man, John Clulow and Russell C. JonesDepartment of Biological Sciences, University of Newcastle, NSW2308, Australia.Michael J McKayPeter MacCallum Cancer Institute, St Andrews Place, Melbourne, AustraliaThe development of DNA microarray technologies over the last few years has heralded a potentialfor providing new, sharp, tools for application to many questions in biology and medicine. At thisrelatively early stage, however, it is unclear as to what the true impact of microarrays, or DNAChips, will be. Various types of microarrays have been developed, including normal tissue- andtumour- derived arrays (generated from pathological specimens) and proteomic approaches. Thispresentation will focus on mRNA-based systems, with a particular emphasis on RNA expressionprofiling and some of the strategies and common pitfalls which might be considered by thoseplanning microarray experiments. Other applications of RNA microarrays will be brieflyconsidered.Two main RNA microarray strategies are now in relatively common use. These are oligonucleotidearrays, typically based on photolithographic deposition of DNA on silicon, and arrayed cDNAs,derived from known genes or expressed sequence tags (ETSs). eDNA arrays can comprise completeor partial cDNA fragments.Some work towards developing mRNA-based microarrays in Australia will be discussed, illustratedby specific research questions, mainly in the field of cancer, to which microarray analysis is beingapplied.IntroductionRecent work has shown that the ductuli efferentesare essential for male fertility (1). We have shownthat the ductuli reabsorb 96% of the fluid leavingthe testis and that the reabsorption is dependent onfluid flow rate and Na+ concentration of theperfusate(2,3). Our previous studies havedemonstrated that luminally adminstered cAMPsuppresses fluid reabsorption in the ductuliefferentis (4), indicating that the cAMP signaltransduction pathway is involved in controllingfluid reabsorption in the ductuli of the rat. In thehomologous proximal kidney tubule, cGMP hasalso been reported to reduce tubular reabsorption(5). The current study was undertaken to determinewhether cGMP has an effect on the fluidreabsorption in the ductuli efferentes.Materials and MethodsMicroperfusion experiments were performed onanaesthetized male Wister rats. A length ofefferent duct was isolated and perfused withKrebs-ringer bicarbonate solution containingdifferent concentrations of dibutyryl-cGMP at arate of 0.1 JlJ.min- 1 • The reabsorption rate wascalculated from the volume difference between theperfusate and collectate divided by the length ofthe perfused duct. Electrolyte composition in thecollectate was determined by energy-dispersivespectroscopy.ResultsTable 1 shows that the fluid reabsorption in theductuli efferentes is not significiantly changed by0.1-1.0mM dibutyryl-cGMP in the luminalperfusate. cGMP has no effect on reabsorption atconcentrations at which cAMP completelyabolishes reabsorption. Futhermore, there is nosignificant difference in the concentrations of Na+,K+ and cr , the major luminal ions, in thecollected fluid between the control and dibutyrylcGMP-treatedgroups (Table 2).DiscussionOur results strongly suggest that cGMP is not thesecond messenger mediating fluid regulation in theductuli efferentes. By contrast, both cGMP andcAMP are reported to mediate fluid reabsorptionin the proximal renal tubules (6,7). The Na+/H+exchanger has been reported as one of theprincipal transporters responsible for fluid andelectrolyte reabsorption in the ductuli efferentes(8) and its function could be regulated by cAMP asin the proximal tubules.Table 1. Effect of Dibutyryl-cGMP and DibutyrylcAMPon Fluid Reabsorption in Perfused RatDuctuli Efferentis. Mean + S.. E M ., * P