Dietary-induced increase in lactase activity and in immunoreactive lactase in adult rat jejunum

Abstract

Adult rats that had been fed on a low-starch high-fat diet for 7 days were force-fed with either the same diet or isoenergetic diets containing 40% of energy as either sucrose or lactose. Within 12 h, the increase in jejunal lactase activity in sucrose-and lactose-fed rats was accompanied by a corresponding increase in immunoreactive lactase protein.Activity of lactase in adult rat jejuno-ileum responds to increased intake of various carbohydrates, including starch and sucrose (McCarthy et al., 1980;Bustamante et al., 1981; Yamada et al., 198 1a,b), with a rapid increase. The possibility that such increases are due to increases in the amount of lactase protein was investigated in the present paper. Changes in amounts of lactase protein accompanying increases of lactase activity were determined by immunological methods in jejunum of rats fed on sucrose or lactose diets. Materials and methods AnimalsFemale Sprague-Dawley rats born in our animal colony were weaned at 30 days of age and fed on standard laboratory chow (Lab Blox; Allied Mills, Chicago, IL, U.S.A.) until 60 days of age. At that time they were fed on a synthetic low-starch (5% of energy) high-fat (73% of energy) diet for 7 days (Yamada et al., 198 la). To control the food intake, they were then force-fed (via a plastic tube) with the low-starch diet or an isoenergetic sucrose diet or an isoenergetic lactose diet [40% of energy as sucrose or lactose, 37% of energy as fat and 22% of energy as protein, diluted with distilled water to make 9.9kJ/ml (2.36kcal/ml)]. Since decreased food intake or starvation can influence the specific activity of lactase (Ecknauer, 1978;Yamada et al., 1983), we considered it important to control the food intake by force-feeding. Force-feeding was performed three times in 12 h: at 22: 00, 02:00 and 06:00 h. The amount of diet was 6ml per feeding, providing 88kJ (21 kcal)/lOOg body wt. per 12h, * To whom reprint requests should be addressed. which corresponds to two-thirds of daily energy intake for rats of this age (Hahn & Koldovsk'y, 1967). This was considered adequate, because during the night hours rats in our animal colony consume about two-thirds of their daily intake.Rats had free access to water. The rats were killed by decapitation at 10 :OOh, i.e. 12h after the initial feeding of the sucrose and lactose diets. Preparation of intestinal samplesThe entire intestine was removed. The duodenum was discarded, and the jejuno-ileum was divided into three equal parts along its length. The proximal third of the jejuno-ileum (upper jejunum) was flushed with ice-cold saline (0.9% NaCl), and the mucosa was scraped from the remainder with a glass slide.

Metabolic effects of dietary lactose in adult female rats

“…There are multiple reports of dietary-induced increases in intestinal lactase activity and enhanced lactose absorption with dietary manipulation [32,33]. Rat lactase protein expression can be induced by a lactose-rich diet [34]. Based on these reports, it is apparent that lactase is an adaptive enzyme that may be induced by lactose loading in animals.…”

Aspects moléculaires de l'adaptation des enzymes pancréatiques et intestinales au régime alimentaire

“…Une étude segmentale de la réponse peptidasique mesurée à l'aide du substrat phénylalanylglycine (Mc Carthy, Nicholson et Kim, 1980) (Yamada et al, 1983 ;Ulshen et Grand, 1979). Il semble cependant que l'activité lactasique intestinale soit rapidement (environ 12 h) modulable par un régime hyperglucidique (Goda et al, 1984). Enfin, soulignons le fait que la localisation de la réponse enzymatique le long de l'axe villositaire a été étudiée.…”

Proceedings of the Physiological Society, 18‐19 September 1987, Cambridge Meeting: Communications

“…glucose or galactose) may be responsible for the age-related decline in the intestinal mucosal lactase activity (Goda, Bustamante, Thornburg & Koldovsky, 1984). In a previous communication to this Society it has been shown that continued supplementation of the diet of growing rats with physiological amounts of cow's milk or a 5 % solution of lactose had no effect on the decline of lactase with age (Tadesse, 1987).…”