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

TESTING FOR REPRODUCTIVE TOXICITY 445anus. This distance is larger in the male than female (approximately 3.5 mm versus 1.4 mm). 54 Thetestes are situated in the abdomen of the newborn male and do not descend into the scrotum untilthe rat is 4 to 6 weeks old. When viewed externally, the large testicles make the scrotal sacs protrude.The inguinal canal, unlike that of the human, remains open in the adult rat, so the testes may bewithdrawn into the abdomen. Also visible externally is the aperture of the prepuce. The prepuceis a loose sheath that protects the penis. The penis and the external orifice of the urethra can beexposed for examination by gentle backward pressure at the sides of the prepuce.B. ObservationsThere are three basic types of observations performed by trained technicians: a viability check, aclinical observation, and an extended or detailed clinical observation. A viability check is a dailycage-side observation performed once (at the start of the workday) or twice (at the start and endof the workday) to determine mortality, morbidity, early delivery, or abortion. During the viabilitycheck, food and water availability should also be monitored. The clinical observation is a moredetailed evaluation of the physical or behavioral characteristics of the rat. The rat is removed fromthe cage and observed for any abnormalities, physical or behavioral. This observation is usuallyperformed prior to treatment and often at a selected interval after treatment. The extended or detailedclinical observation is performed in an open field arena by a technician trained to administer theFOB. The extended or detailed clinical observation is essentially a FOB without including forelimband hind limb grip strength, hind limb foot splay, and body temperature measurements (see below).Extended or detailed clinical observations are usually performed weekly or monthly dependingupon the protocol.C. Male Body Weight and Food ConsumptionBody weights are recorded daily, twice weekly, or weekly, depending upon the guideline requirements.Food consumption is usually recorded at the same interval as body weight. Body weightand food consumption should be recorded at approximately the same time of day during the courseof the study. Recording male body weight during treatment provides an indicator of the generalhealth status that may be relevant in the interpretation of male reproductive effects. Body weightloss or reduction in body weight gain can be caused by several factors, including systemic toxicity,stress (such as restraint), treatment-induced anorexia, or decreased feed or water consumption dueto altered palatability. Caloric restriction studies that caused small reductions in body weight haveshown little effect on the male reproductive organs or function. 55 If a direct link between bodyweight change and the male reproductive effect cannot be established, then male reproductivesystem alterations should be considered adverse reproductive effects and not secondary to theoccurrence of systemic toxicity. However, in the presence of severe body weight change or othersignificant systemic toxic effects, it should be stated that an adverse effect on a male reproductiveendpoint occurred, but the effect may have resulted from a systemic toxic effect.D. Male NecropsyThe male is usually terminated after the cohabitation period; however, it may be advisable tocontinue treatment and delay termination until after pregnancy outcome is known. In the event ofan equivocal effect on fertility, the treated males can be mated with untreated females to determineif the effect was male mediated. The male is euthanized and subjected to a complete necropsy. Thereproductive organs, and other tissues specified in the protocol, are weighed and saved for possiblehistopathological evaluation. At necropsy, sperm quality may also be assessed (see below).© 2006 by Taylor & Francis Group, LLC