Gerald W. Scott

Contractility of human gallbladder muscle in vitro

This study examined the effects of transmural nerve stimulation, acetylcholine, adrenoceptor agonists and several peptides on the contractility of strips of human gallbladder in vitro. Acetylcholine caused concentration‐related contractions of the tissues and the sensitivity to acetylcholine was similar in gallbladders with mild and severe chronic cholecystitis. Noradrenaline and adrenaline relaxed gallbladder strips, probably via β2‐adrenoceptor stimulation. Transmural nerve stimulation always caused contractions, but in the presence of atropine inhibitory responses were demonstrable and these were antagonized by propranolol. There was no evidence of non‐adrenergic inhibitory neural responses. Of the peptides tested, only cholecystokinin octapeptide (CCK‐OP), gastrin, pentagastrin, substance P and caerulein caused contractions. Responses to CCK‐OP, gastrin and pentagastrin were antagonized by dibutyryl cyclic GMP. Hormones which had no effect upon human gallbladder strips included motilin, secretin, bombesin, neurotensin, glucagon, vasopressin, VIP and somatostatin. Considerable differences therefore exist between human tissues and those from experimental animals with respect to the direct actions of neural and hormonal stimuli on gallbladder contractility.

Morphology of canine gallbladder

SummaryExamination of the surface topography of canine gallbladder epithelium using the scanning electron microscope reveals subtle changes in the morphology of the cellular components between the full and empty states. In the full state large bays exist between relatively low, ridge-like crests or folds of mucosa which gradually increase in height as the gallbladder empties causing a subsequent reduction in size and volume of the bays. The relaxed gallbladder exhibits an irregular arrangement of tall, closely apposed mucosal folds with intervening deep valleys. The degree of apical convexity of individual epithelial cells will increase as the mucosal folds begin to relax. Other mucosal features most easily observed in the full state were small pit-like intraepithelial glands. The apical surfaces of the epithelial cells exhibit a densely uniform microvillus border and occasional membrane-bounded cytoplasmic protrusions (apical bullae) extending out into the lumen of the organ. The lateral cell membranes and basal lamina were also examined. Correlative methacrylate and transmission electron microscopic findings are included. The functional aspects of these morphological alterations and apical protrusions are discussed.

Adenosine and ATP effects on isolated guinea pig gallbladder

The effects of adenosine, ATP and several derivatives of adenosine were measured in isolated strips of guinea pig gallbladder. Adenosine caused relaxations which were antagonized by theophylline and potentiated by an inhibitor of adenosine uptake, 6-(1-hydroxy-5-nitrobenzylthio)-guanosine (HNBTG). Among several adenosine derivatives, 2-chloroadenosine and 5′-N-ethylcarboxymidoadenosine were similarly effective while 1-N6-phenylisopropyladenosine was only a weak relaxant. None of the derivatives caused maximal relaxations at 100 μM, and thus absolute potencies could not be determined. ATP caused predominantly contractile effects, with relaxations sometimes being evident at high concentrations. Indomethacin abolished contractile effects of ATP, suggesting prostaglandin involvement, and only relaxations were evident in its presence. Adenosine deaminase abolished the effects of adenosine and partly reduced the relaxant effects of ATP in the presence of indomethacin. In view of the low potency of adenosine and ATP, physiological roles for these compounds in gallbladder motility are not readily evident.

Ultrastructural Observations on the Gallbladder of Richardson’s Ground Squirrel (Spermophilus richardsonii)

The gallbladder of Richardsons ground squirrel shares many structural similarities with numerous other species, including the mouse, rabbit and man. Dark cells exhibit a condensed cytoplasm but contain all the typical organelles of light cells, although their total complement appears reduced. Edematous cells extruded from the epithelial lining were replaced through mitosis or had their space occupied by adjacent cells. Specializations of the basal plasma membrane and underlying basal lamina form peg-and-socket interdigitations, and desmosomes were observed on the lateral cell boundaries down to the level of the basal lamina. The latter remain intact during active water resorption while the former disappear. Adrenergic nerve fibers were observed intramuscularly and beneath the basal lamina. Random interepithelial migration of leucocytes was also observed. Some of these observations help to elucidate controversial issues whereas others have been previously unreported and may be species-dependent.