Ketogenic diet decreases circulating concentrations of neuroactive steroids of female rats

Abstract

Ketogenic diet (KD) is used to manage intractable epilepsy; however, the mechanisms underlying its therapeutic effects are not known. Steroid hormones, such as progesterone and testosterone, are derived from cholesterol, and are readily 5alpha-reduced to dihydroprogesterone and dihydrotestosterone, which are subsequently converted to 5alpha-pregnan-3alpha-ol-20-one (3alpha,5alpha-THP) and 3alpha-androstanediol, neuroactive steroids that can influence seizures. The present study examined the effects of the KD on circulating concentrations of these neuroactive steroids, and their precursors, in intact female rats. Thirty-six, 22-day-old female Sprague-Dawley rats (weaned at 21 days) were fasted for 8 hours prior to placement on one of three dietary regimens for 6 weeks: ad libitum chow, calorie-restricted chow, or KD. After 6 weeks of the diet, when six rats in each dietary condition were in diestrus and six were in behavioral estrus, all rats were administered pentylenetetrazole (PTZ, 70 mg/kg, i.p.). The latency and incidence of seizures were recorded by an observer who was uninformed of the estrous cycle and dietary treatment conditions of the rats. Immediately after each test, trunk blood was obtained for later measurement of pregnane (progesterone, dihydroprogesterone, 3alpha,5alpha-THP) and androstane (testosterone, dihydrotestosterone, 3alpha-androstanediol) neuroactive steroid concentrations in plasma by radioimmunoassay. KD tended to lengthen the latency to, and significantly reduced the number of, PTZ-induced barrel roll seizures. KD also significantly reduced plasma levels of the pregnane (dihydroprogesterone, 3alpha,5alpha-THP) and androstane (dihydrotestosterone, 3alpha-androstanediol) 5alpha-reduced metabolites. These data suggest that levels of pregnane and androstane neuroactive steroids, or their precursors, may underlie some of the antiseizure effects of KD.

Fig. 1

Mean (± SEM) latencies to (top) and incidence of (bottom) pentylenetetrazole-induced seizures of rats on ad libitum (left, white), calorie-restricted (middle, black), and ketogenic (right, striped) diets. ^#Tendency (P = 0.08) for latencies to be longer for rats on the KD. ^*Number of seizures was significantly lower (P = 0.01) for rats on the KD.

Fig. 2

Mean (± SEM) plasma progesterone (top), dihydroprogesterone (middle), and 3α,5α-THP (bottom) levels for rats on an ad libitum (left, white), calorie-restricted (middle, black), and ketogenic (right, striped) diets that were administered pentylenetetrazole. ^#Tendency for 3α,5α-THP levels to be lower in rats on the KD compared with caloriere-stricted diet. ^*Dihydroprogesterone and 3α,5α-THP levels were significantly lower in rats on the KD than in rats on an ad libitum diet.

Fig. 3

Mean (± SEM) plasma testosterone (top), dihydrotestosterone (middle), and 3α-androstanediol (bottom) levels for rats maintained for 21 days on ad libitum (left, white), calorie-restricted (middle, black), and ketogenic (right, striped) diets that were administered pentylenetetrazole. ^#Tendency for dihydrotestosterone or 3α-androstanediol to be lower in rats on the KD compared with the calorie-restricted diet. ^*Dihydrotestosterone and 3α-androstanediol levels were significantly lower in rats on the KD than in rats on an ad libitum diet.