The Melatonin, a close derivative of serotonin, is involved in physiological regulation of circadian rhythms. In the gastrointestinal (GI) system, melatonin exhibits endocrine, paracrine and autocrine actions and is implicated in the regulation of GI motility. Generally, melatonin actions oppose the stimulatory actions of serotonin on motility. However, it is not known whether melatonin can also act directly on GI smooth muscle cells. The aim of the present study was to determine the expression of melatonin receptors in smooth muscle and identify their signaling pathways. Muscle cells were isolated from rabbit distal stomach by enzymatic digestion, filtration and centrifugation and cultured in DMEM-10. Expression of melatonin receptors, MT1 and MT2, was determined by RT-PCR and Western blot. G protein activity was measured by melatonin-induced increase in Gα binding to [35S]GTPγS. Phosphoinositide (PI)-specific phospholipase C (PLC-) activity was measured by ion-exchange chromatography. Cytosolic Ca2+ was measured in fura-2 loaded cells and muscle contraction was measured by scanning micrometry. In cultured gastric smooth muscle cells MT1 was detected by RT-PCR and western blot. Melatonin activated Gαq, but not Gαs, Gαi1, Gαi2, or Gαi3. Consistent with activation of Gαq, melatonin stimulated PLC-β activity (PI hydrolysis), increased cytosolic Ca2+, and elicited muscle contraction. Stimulation of PLC-β activity was blocked by the expression of Gq minigene and contraction was blocked by the PLC-β inhibitor, U73122. We conclude that gastric smooth muscle cells express receptors for melatonin (MT1) coupled to Gq. The receptors mediate stimulation of PLC- activity and increase in cytosolic Ca2+, and elicit muscle contraction.

FundaÃÃo de Amparo à Pesquisa do Estado do Cearà / Objetivos: A hipovolemia aguda reduz o tÃnus e aumenta a complacÃncia gÃstrica em animais. A complacÃncia do estÃmago proximal à o principal determinante da saciedade no teste de saciedade (drinking test). No entanto, nÃo hà relatos de eventuais alteraÃÃes de complacÃncia, tÃnus, saciedade e de plenitude gÃstricas frente a uma reduÃÃo aguda do volume sangÃÃneo em humanos. MÃtodo: ApÃs aprovaÃÃo pelo Comità de Ãtica, e seguido de jejum noturno de 8 horas, estudou-se 23 voluntÃrios sadios. TÃnus e complacÃncia: ApÃs obtenÃÃo de um acesso venoso, uma sonda-balÃo (12F, saco de PVC de 1600ml) foi afixada no estÃmago proximal dos voluntÃrios (n=17). O volume gÃstrico foi medido continuamente por um sistema computadorizado de barostato (SynecticsÂ), com a pressÃo intragÃstrica fixada em 12mmHg. ApÃs um perÃodo basal de 30min os voluntÃrios foram submetidos aleatoriamente a sangria (doaÃÃo padrÃo de sangue, 450 ml) ou apenas a punÃÃo venosa. Foram realizados tambÃm pequenos aumentos da pressÃo intra-balÃo atà o relato de leve desconforto, antes do perÃodo basal e ao final do estudo. Em sete voluntÃrios foi realizada infusÃo de salina 15min apÃs a sangria. Saciedade e plenitude: Avaliou-se seis voluntÃrios sadios (homens, 28,5Â3,5 anos) em duas ocasiÃes (intervalo de 1 a 2 semanas). ApÃs jejum noturno de 8h, os voluntÃrios ingeriram refeiÃÃo padronizada. Decorridas 2h, foram submetidos à punÃÃo venosa seguida (condiÃÃo experimental) ou nÃo (controle) por doaÃÃo padrÃo de sangue. Logo apÃs, avaliou-se a saciedade e a plenitude gÃstricas pelo drinking test modificado mediante a ingestÃo de refeiÃÃo lÃquida, achocolatada sem lactose, num ritmo fixo de 15 ml/min. A cada 5min da refeiÃÃo teste, avaliou-se a plenitude utilizando escala de 0 a 5 (0-nÃo sinto nada, 5-nÃo agÃento mais) e a saciedade com escala de descritores. Resultados: A sangria causou um aumento no volume gÃstrico (incremento sobre o perÃodo basal: 154  62ml aos 5min e 152  66ml aos 30min, p < 0,05). A inclinaÃÃo da curva volume vs pressÃo aumentou apÃs doaÃÃo de sangue (53,7  4,2 vs 45,1  4,2ml.mmHg-1 basal, p = 0,01). A infusÃo de salina trouxe os valores de volta ao nÃvel basal (0 ml basal vs -14  6 ml aos 30min, p > 0,05). A doaÃÃo padrÃo de sangue aumentou o volume mÃximo ingerido em relaÃÃo à condiÃÃo controle (790Â56,7 vs 1327Â127ml, p<0,05). O tempo para chegar ao valor 5 (plenitude mÃxima) foi maior apÃs doaÃÃo de sangue (52,8Â4 vs 95,8Â8min, p<0,05). O tempo para a primeira sensaÃÃo (âcomeÃando a encherâ) e o tempo para a terceira sensaÃÃo (âcheioâ) foram maiores apÃs a doaÃÃo de sangue (19,2Â1,3 vs 41,6 Â4,2min e 37,8Â3,5 vs 67,5  6,6min, respectivamente, p<0,05). A doaÃÃo de sangue nÃo alterou significativamente a pressÃo arterial e a freqÃÃncia cardÃaca. ConclusÃo: A doaÃÃo de sangue diminuiu o tÃnus e aumentou a complacÃncia gÃstrica. A infusÃo de salina reverteu esse fenÃmeno. A reduÃÃo da volemia aumentou o limiar para a percepÃÃo da plenitude gÃstrica. Isto pode corresponder a um novo fator determinante de sintomas relacionados à plenitude gÃstrica. / Introduction: We have shown that blood shedding reduces tonus and increases gastric compliance in animals. Since satiety to a drinking test is affected by gastric tonus and compliance, we investigated the effect of blood donation (BD) and saline infusion in gastric tonus, compliance and sensitivity in healthy volunteers. Method: After approval of local ethics committee, 23 healthy male volunteers were studied. After an overnight fast (8-10h), followed by a light meal, and a 2h interval, one of the following procedures was performed. Tonus and compliance study. A PVC bag (1.6L) attached to a catheter was placed into the proximal stomach. Gastric volume (GV, ml) was continuously measured by an electronic barostat (SynecticsÂ), with the intrabag pressure fixed at 12mmHg. After 30-min basal recording, the subjects (n=18) were randomly submitted to either BD (450 ml) or venous puncture site manipulation only, and GV was recorded for further 30-min. Small IP increments (until mild pain report) were also performed; before the basal period and at the end of the study. In 5 volunteers, saline infusion (1.3L) was performed 15-min after BD. Satiety. Volunteers were studied in two different occasions, 1 to 2 weeks apart. They were submitted to a blood donation or venous puncture only, before a modified satiety drinking test with a caloric meal was performed. Results: BD caused a rapid increase in GV (values above basal levels: 154  62 ml at 5 minutes after shedding start and 152  66 ml at the end of study, p<0.05). Volume x pressure slope increased (53.7  4.2 vs. 45.1  4.2ml.mmHg-1 basal, P=0.01) after BD. Saline infusion brought GV back to basal levels (0Â1 ml basal vs -14  6 ml at 30 min). BD increased the maximum volume ingested by the volunteers (790Â56,7 vs. 1327Â127ml, p<0.05). The time to reach the maximum score was also increased. (52.8Â4 vs. 95.8Â8min, p<0.05). The time to elicit the first (beginning to feel full) and third (full) sensations was also increased after BD (19.2Â1.3 vs. 41.6 Â4.2min e 37.8Â3.5 vs. 67.5 Â6.6min, respectively, p<0.05). BD did not change blood pressure and cardiac rate. Conclusions: BD decreases gastric tonus and increases gastric compliance. Saline infusion reverted such phenomena. Furthermore BD increases the time and volume sensitivity threshold in a satiety drinking test. This might explain dyspeptic complains in individuals under acute volemic imbalance.

Electrical activity of the stomach is one determining factor of gastric motility by controlling and coordinating contractions of the gastric musculature. These contractions, both tonic and phasic, are responsible for the storing, mixing, and emptying of food. Gastric electrical activity is therefore a very important factor for normal stomach function. The development of a multi-channel, bandlimited, signal amplifier and recording system, provides a means to record this electrical activity. Many practical issues are addressed to provide a signal of acceptable quality and several basic signal processing techniques are applied to increase the quality of these signals and provide extraction of important information regarding power and frequency content. Gastric electrical activity is recorded from the stomachs of several rats in various experiments. The recorded activity in different regions of the stomach, responsible for different functions, is compared and evaluated with respect to known cellular events. By introducing several stimuli and observing changes in recorded activity, the nervous control of the stomach via mediation of the electrical activity is also examined and modeled briefly. / Thesis / Master of Engineering (ME)