A Practical Approach, Second Edition=Ronald D. Ho.pdf

Human Non-human Primate Rat Dog MouseSeminal Vesicles (SV)SpermatozoaLeydig CellsThe SV are present bygestational month 6 andhave attained adult formby the 7th month ofgestation. Developmentof the muscular wall ismediated by estrogenstimulation. Growth ofthe SV continues slowlyuntil puberty. 66 Secretoryactivity of the SV isandrogen dependent. 95Spermatogonia increase6-fold between birth and10 years of age, thenincrease at puberty.Mean age at spermarcheis 13.4 years; ejaculationpossible during middle tolate puberty. 1,8,13,16Testosterone (T)producing cells, Leydigcells (LC), beginproducing T ~7-8 weeksof gestation 96 andultimately come undercontrol of placentalgonadotrophin (humanchorionic gonadotrophin,hCG). 97 Pituitarygonadotrophin synthesisbegins at ~ 12 weeks ofgestation after Tproduction begins. 98In the testis,spermatogonia becomemore numerous by theend of the 1 st year.Spermatozoa in thetestis appear as early as3 yrs with fertility startingat approximately 3.5yrs. 17,19LC are prominent in fetallife but decrease innumber during the 1st yrand dedifferentiate. Bythe end of 3 yrs the LCsredifferentiate. T levels inimmature males is ~30-250 ng/100 ml rising to230-1211 ng/100ml inmature males. 18The basic pattern of theSV are present at PND10, with lumen formationfrom PND 2-15 andmarkedly increasing insize between PND 11-24with adult appearanceand secretory propertiesbetween PND 40-50. 84Secretory granules areevident at PND 16.In seminiferous tubulesPND 45, 31 in vasdeferens PND 58-59. 32Spermatogenesis isstimulated by increasedtestosterone andgonadotrophinproduction.Testosterone productionbegins during lategestation and decreasesjust prior to birth. Duringthe infantile-juvenileperiod (PND 8-35) theprimary androgensproduced includeandrostenedione, 5alpha-androstanediol,and dihydrotestosteroneNOT testosterone 105,106but by ~PND 25 andonward testosteronebecomes the primaryandrogen 105,107 Differentandrogen levels areprimarily due to changesin steroidogenic enzymelevels or activity.The dog has neither SVnor bulbourethralglands 73In testis at 26-28 wks ofage. First visible in theepididymis 26-28 wks(beagles 41 ); first inejaculate 32-34 weeks(fox terriers 52 )First visible histologicallyGD 36-46. 39 TesticularLH receptors begin toincrease at 2 mos., reachmax. 12-24 mos. Testic.T and DHT levels beginto increase at 6 mos.,plateau 12-24 mos(beagles 128 )LCs proliferation isdependent ongonadotrophin and ends~ PND 21-33 33POSTNATAL DEVELOPMENTAL MILESTONES 1031© 2006 by Taylor & Francis Group, LLC