The Effects of Niacin on Serum and Labyrinthine Electrolyte

Abstract

The word “niacin” is the general term for nicotinic acid, nicotinam ide and other nicotinic acid derivatives. Especially, nicotinic acid is the most useful drug for Ménière's disease, tinnitus and other diseases of inner ear. But the pharmacological action of these drugs is not so clear, and there is considerable divergence of view about the vasodilative effect on the intracranial vein. When we use nicotinic acid or other derivatives clinically, we often find its remedial value manifested after the cessation of its administration. Also the value does often appear in the case of nicotinamide administraion. These facts are difficult to explain only by the vasodilative effect.
The author's experiments started from the question if these values are attributable to the original effect of niacin as a co-dehydrogenase.
First, we must pay attentio n to the problem of niacin deficiency in the disturbances of inner ear, as Atkinson reported on Ménière's disease. But the author's results denied the niacin de ficiency on Ménière's disease and sensory neural deafness, though a little remains unsettled (Table 1, 2).
Secondly, the author found the suppressive effect of niacin on the serum pottasium fluctuation in the administration of pottasium chloride and the noise exposure.
In the experiment with rabbits, the serum pottasium value increased by about 1.3 meq/l in the administration of 0.5g pottasium chlorlde, but did not increase in the case that some niacin (nicotinic acid 20mg or nicotinamide 25mg) was simultaneously administrated (Table 3, 4). This effect was more remarkable in nicotinamide administration and the excretion of pottasium in urine did not increase but rather decreased three hours after the administration of pottasium chloride (Table 4, 5).
With guinea pig s, the noise exposure for five hours increased the value by about 1 meq/l, and the five days exposure for five hours a day decreased it in the same degree (Table 7, 8). But in the cases of niacin administration before noise exposure these fluctuations disappeared as with rabbits.
The author observed the Stria vascularis of guinea pigs, and succeeded in staining the pottasium in it by means of the McCallum's method with frozen procedure as Kawata and Takeda had adopted.
By this method, the Stria vascularis of normal guinea pigs was better stained than the Ligamentum spirale and they were clearly distinguished from each other. With the animals exposed to noise for five days, the borders between the Stria vascularis and the Ligamentum spirale became indistinct. Moreover, this change was limited in the upper part of basal turn and the lower part of second turn of the cochlea. While the animals which were given niacin (nicotinamide 25mg) before the noise exposure did'nt cause this change in the Stria vascularis. The changes were also observed in the animals which were exposed to noise for ten days or fifte en days, and were still limited in the same regions of cochlea, but in these cases the effe ct of niacin was not certain. In the latter cases the border between the Stria vascularis and the Ligamentum spirale became somewhat indistinct, as in the case of noise exposure without niacin.
Judging from these results, this effect of niacin must have continued for five days at the longest, under this condition of noise. This effect was also uncertain in the administration of niacin with the therapeutic purpose. The animals were exposed to noise for seven days, and divided into two groups. After the noise exposure some of the one group were given niacin for three days, some five and others seven, and the other group was all left undone. But there we re no clear difference between the two groups. In either case the change in the Stria vascularis was recovered in a remarkable degree.