STUDIES ON FLUORINE IN THE NUTRITION OF THE RAT

Abstract

I. The evidence obtained from birth weights, weaning weights, and growth records indicates that small doses of F inhibit normal growth. Daily intakes of approximately 20 mgm. F per kgm. of body weight in the form of NaF and 40 mgm. F per kgm. of body weight in the form of rock phosphate appear to be the upper limits of safety for growth. The toxicity of the F in CaF2 is much less than that of the Na salt and it seems to be of a similar magnitude to the toxicity of the F in rock phosphate. Typical effects of F upon the incisor teeth were produced even at the lowest levels fed, and this effect appears to be the most obvious and constant macroscopic index of F toxicosis in the rat.[long dash]II. Evidence is submitted that chronic F poisoning does not inhibit reproduction; any unfavorable effect upon reproduction arises secondarily as the result of a systemic reaction to F. The estrous cycle is not disturbed by low levels of NaF compatible with normal growth. If the dosage is raised beyond the threshold value of 25 mgm. of F per kgm. of body weight per day suppression of estrum occurs. Inanition has been shown to be the cause of the suppression of estrum when this amount of F is fed as NaF. The fresh weight of the suprarenal glands is increased by including F in the ration. There is some evidence that the increase in weight of the glands is more pronounced when higher levels of F are used. Lactation is suppressed by F when fed in amounts above the upper limit of safety for the rat. Similarly the rate of reproduction is sharply reduced when this limit of intake is exceeded. Coincident with this systemic action is a reduced intake of food. No clear-cut and positive evidence is available to show that chronic F poisoning has a cumulative effect upon reproduction or other physiological processes from generation to generation for as long as five generations. The gonad-stimulating potency of the anterior lobe of the hypophysis was unimpaired by the intakes of F fed.