Gastric pathologic and biochemical changes induced by starvation of weanling rats

LiYe Soienoes Yol. 5, pp . 509-519, 1966 . Printed in Great Britain .

Pergamon Press Ltd.

GASTRIC PATHOLOGIC AND BIOCHEMICAL CHANGER IIdDUCED BY STAR~%ATION OF WEAKLING RATS C. J. Pfeiffer, J. R. Debro, and P. J. Muller Blotechnolo® Division Ames Research Center, NASA Moffe~t Field, Calif. (Eeaeived 5 Fovember 1965 ; in final Yorm 21 January 1966) Introduction The appearance of lesions in the glandular portion of stomachs of mice following total, short-term starvation has been reported by several investigators (1, 2) .

However, the near complete lack of such glandular, hemorrhagic

erosions in the rat following similar starvation (1-4 days) has been reported, although crater-shaped lesions and edema appear to be commonly observed in the forestomach (squamous regloa) of fasted rats (3-8).

In addition, numer-

ous nutritional studies have reported the appearance of lesions in the intestine, the forestomach, and the glandular stomach of rats, but these studies have usually been characterized as chronic experiments involving selective vitamin or nutritional deficiencies (?-14) .

It has been suggested that the gastric glan-

dular lesions of mice fasted for three days may simply be a manifestation of a high metabolic rate - known to accompany decreasing mammalian size (15,18) - and that the lower metabolic rate of rata prolongs the development time required for pathogenesis of glandular lesions in the stomach.

The fact

that chlorpromazine represses glandular ulceration as well a.s activity in fasted mice (2) further suggests a metabolic rate factor in ulcerogenesis . Since previous experiments in this laboratory indicate that weanling (21 day) rats demonstrate more severe stress responses to chronic restraint than adult rats (17), the following procedures were conducted to 1) compare the gastric response of weanling rats subjected to starvation to that of postweanling rats, and 2) elucidate these responses by examining several stress 509

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responsiveparameters of the organism (thymic involution, relative adrenal weight, etc. ) and of the tissue involved (gastric mucosal hexosemonophosphate shunt enzymes) . Materials and Methods Male Sprague-Dawley rats (Berkeley Pacific Laboratory) were utilized for all experiments, and were housed individually in wire-bottom cages and fed Purina Laboratory Chow.

A total of 272 animals wére used, and all animals

were weaned at 21 days . During starvation experiments all food was removed for 2-5 days (water administeréd ad libitum) and rats were sacrificed by intracranial ethanol on the day following the last day of fasting.

The specific dura-

tions of fasting are given in Table 1, and the specific ages of rats used in these experiments are given in Tables 1 and 2. Gross pathology of the forestomach and glandular stomach of each animal was individually assessed in accordance with an ulcer index previously described (5).

This index is based upon the severity and number of lesions; a

normal stomach is rated 1, and the highest possible rating is 15 . The activity of the gastric mucosal hexosemonophosphate* shunt, a stresaresponsive enzyme system (18) of significant activity in the gut mucosa (19), was estimated by assaying the two NADP* -dependent enzymes of the shunt, glucose-6-phosphate dehydrogenase* and 6-phosphogluconate dehydrogenase.* Homogenates of gastric glandular mucosae were prepared from individual animals in a manner previously described (20) . Centrifuged (500 x G, 20 min), cell-free suspensions of each sample were assayed for the dehydrogenases by the Fitch, Hill, and Chaikoff modification (21) of the method of Glock and McLean (22) .

The rate of reduced NADP formation was measured at 340 m~.

by means of a Beckman DU2 Spectrophotometer. Enzyme activities in samples * The following abbreviations will be employed in the text, tables, and figures: HMP, hexosemonophosphate ; NADP, nicotinamide adenine dinucleotide phosphate; GBPD, glucose-6-phosphate dehydrogenase; and BPGD, 6phosphogluconate dehydrogenase.

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from each animal were individually assayed and adjusted for the amount of protein in each sample .

Protein content was determined by the method of

Lowry et al . {23) . Statistical analysis of the data was undertaken on an IHM 7094/40 DCS digital computer.

A one-way analysis of variance was performed utilizing

Scheffe' s method (24) of comparison between means with unequal sample size . Differences between means of enzyme values, body, and organ weights were tested at an overall significance level, o = 0. 05.

Comparisons were under-

taken between five-day fed and five-day fasted weanling, and four-day fed a.ad four-day fasted adult and wea.nling rats .

Standard errors of the mean were

determined for ulcer indices, enzyme values, and body and organ weights. Results The results of the experiments are outlined in Tables 1 a,nd 2. ~ is most notable that the gastric response, in terms of gross ulceration, to short-term starvation is different is weanling rats (21 days) than in other young (24-42 days) or older(58-180. days) rats, it is evide~ that starvation induces primarily glandular rather than forestomach ulceration is the weanling rat, but primarily forestomach rather than glandular ulceration is older rats .

Con-

trasts of this age effect are demonstrated by mean ulcer indices of the forestoma.c h and glandular stomach, respectively, of 1. 8 and 5. 3 (Table 1) for weanling rats and 3. 8-ß. 5 and 1. 4-3. 8 (Table 2) for older rats subjected to 4 days of fasting. It is apparent that the magnitude of the ulcer index of the glandular stomach of weanliag rats. increases with the duration of the fast (Table 1 and Figs . 1 and 2). An estimate of carbohydrate traffic in the gastric, mucosal hexosemonophosphate shunt, as assessed by determination of the NADP-dependent enzyme activities in this pathway, indicates that this shunt becomes less active, fol lowing an initial increase in activity (2 days), in rats fasted for 4-5~days . Although both GBPD and 8P® decreased in activity below control values (Table 1) following 5 days of fasting, only GBPD decreased significantly (p < 0. 05), as shown in Fig. 1. It was also apparent that the within treatment

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FIG. 1

Development of~stric lesions and enzyme activity in fasted weanling rats (18 animals per treatmeilot).

Lesion development and thymic involution in fasted weanling rats. Figures at base of columns represe~ number of animals.

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variation of GBPD, indicated by the standard errors of the mean (Table 1), increased with the age of the animal, An analysis of body and organ weights of fasted animals indicated obvious and progressive losses in body weight, variable changes in testicular and absolute adrenal weights, increases in relative adrenal weights (accentu ated by body weight losses), and pronounced decreases in thymic weight due to fasting. Discussion The discrepant gastric response in ulcerogenesie observed between fasted weanling (21 days) and other fasted young or older (24-180 days) rats is interesting, but not surprising in view of the similar discrepancies observed in fasted mice versus fasted rats, respectively (1-8).

However, this study

indicates that the pathogenesis of these lesions does not relate solely to the level of energy utilization of the organism, which has been shown to be higher in young or small mammals (15,18), since the gastric response differential occurs more rapidly than can be reasonably attributed to size, weight, or age differences . Although the weanling rat is rarely used in gastrointestinal ulcer research, these findings suggest that the fasted weanling rat may provide a useful research tool in ulcer research where surgery or the administration of exogenous drugs is undesirable.*

Other investigators (25) have recently

demonstrated that intragastric (transperitoneal) injection of newborn (98 hour rats with drugs constitutes a useit~l procedure for pediatric, toxicologlc research. Also, one early report (28) indicates that 3 days of total fasting produced glandular lesions in young (" jeunes, " age unspecified) rats . The decrease in carbohydrate metabolism, via the gastric mucosal hexoaemonophosphate shunt, which was observed following 4-5 days of total starvation parallels a similar previously observed (18) decrease in this *These and other experiments of fasted, 21-day-old rats indicate that approximately 0-percent and 25-percent mortality rates may be anticipated for 4 and 5 days fasting, respectively .

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pathway in the jejunal mucosa of fasted rats .

Yol . 5, No . 6

In both cases it was observed

that depression of glucose-8-phosphate dehydrogenase activity surpassed that os 8-phosphogiuconate dehydrogenase activity. 81ace the hezosemonophosphate sfimt is a primary site for generation of pentose units, which are required for nucleic acid synthesis - an eztremely important function of the gut mucosa - a decrease in activity of this shunt may be related to decreased mucosal resistance and/or the pathogenesis of hemorrha~c lesions . In this connection, Volokhonskaya (27) has reported increased turnover rates of nucleic acids, acid-eoluable phosphorus, phosphoproteins, and adenosine triphosphate in the gastric mucosa of fasted rabbits. In addiüon, it was observed that the dehydrogenase activities reported here for gastric tissue were much lower than dehydrogenase activities previously observed is jejunal mucosa (18).

Numerous other investigators

have similarly reported activity and concentration variations is nondlgestive (28-30) and hydrolytic (91) mucosal enzymes throughout the length of the mammalian stomach and intestine. An initial increase in activity of both dehydrogenases was observed (2-4 days) in fasted rats .

ä is impossible to determine in the present experi-

mental design whether or not this initial increase in activity is a normal phenomenon relating to age, or is induced by fasting,

û is important to con-

sider, however, is the interpretation of both enzyme activities and localisation of lesions, that the sudden transition from the all-milk diet to the laboratory chow diet at weaning may inilueace these parameters .

Indeed,

other reports have substantiated the distinction between gastrointestinal enzymic (32, 93) and absorptive (94, 35) phenomena observed in embryos and infants and those observed in adult animals. The analyses of weights of stress-responsive organs of fasted rats indicate that the animals were subjected to'considerable stress .

Extreme

thymic involution, which affords an accurate physiologic index of response to stress (38), occurred in fasted weanliag rats (Fig. 2) . In addition, the

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increases in relative adrenal weights and testicular atrophy support this conclusion (37-40) .

Increases in absolute adrenal weights and decreases in

relative adrenal weights occur normally with age (41); although absolute values for these parameters at different ages are incomparable, the data here (Table 2) demonstrate stress-related changes (17). Summary A differential response of weanling rats (21 days) versus post-weaned rats (24-180 days) to short-term starvation has been observed in the gastric mucoea . Starvation induces ulceration in the glandular mucoea but not in the forestomach of 21-day-old rats, and a reversal of this susceptibility to ulceration occurs in older rats.

The development of glandular lesions in

weanling rats progresses with thè duration of the fast, and parallels thymic involution, increases in relative adrenal weight, and other stress responses. Gastric mucosal, glucose-8-phosphate dehydrogena.se decreases significantly at the fifth day of fasting .

It is suggested that the fasted weanling rat may

afford a useful tool in experimental gastroenterology, and that the development of gastric glandular lesions may relate to impaired carbohydrate metabolism of the mucoea. Acknowled~nents The authors are most grateful to Mr. Eugene Auerkin for his assistance with the statistical analyses . References 1.

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2.

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