EFFECTS OF FEEDING AND SHORT-TERM FASTING ON WATER AND ELECTROLYTE TURNOVER IN FEMALE MINK (MUSTELA-VISON)

Daily (24 h) rates of water and electrolyte turnover were measured in a conventional balance study in ten adult female pastel mink (Mustela vison) given free access to a standard mink feed for a 1-week conditio ning period, followed by a 4 d experimental period and a 2 d fasting p eriod. Drinking water was available throughout. In addition, the compl eteness of urine collection and the fraction of urine collected with t he faeces were determined using a new experimental technique based on 24 h recoveries of specific urinary markers such as tritiated p-aminoh ippuric acid ([H-3]PAH) or C-14-labelled inulin ([C-14]IN) continuousl y delivered by small Alzet(R) osmotic pumps implanted intraperitoneall y. During feeding the mean individual percentage recovery in urine of [H-3]PAH released from the osmotic pumps ranged from 68 to 88% (median 78%). The mean percentage of urinary [H-3]PAH recovered from faecal c ollections was 6% (range 3-12%). In response to fasting the mean indiv idual percentage recovery of [H-3]PAH in urine ranged from 62 to 78% ( median 68%). For urinary [C-14]IN the mean percentage recoveries in fe d and fasted animals were 79 and 63% respectively. Furthermore, during fasting, withdrawal of the supplies of dietary water caused a slight but insignificant (P = 0.17) increase in the daily intake of drinking water and, hence, the animals maintained their normal water balance by a dramatic reduction in urine excretion (P < 0.001). At the same time urinary solute excretion declined significantly (P < 0.001), due in p art to the cessation of dietary electrolyte intake and in part to redu ced formation of urea, whereas urinary osmolality decreased only moder ately. The mean 24 h balances of Na, K, Ca, Mg, Cl and P were close to zero and only minor differences between the feeding and fasting perio ds were observed. When corrected for the measured inaccuracies in urin e collection the balance data obtained in the present study represent useful reference standards for normally fed and fasted non-growing min k and, to some extent, useful guidelines for future studies in experim ental animals.