In vitro effects of substance P analogue [D-Arg1, D-Phe5, D-Trp7,9, Leu11] substance P on human tumour and normal cell growth

Analogues of the neurotransmitter substance P (SP) can interact with neuropeptide receptors, and are reported to inhibit growth of small cell lung cancer cell lines (SCLC CLs). We found [D-Arg1, D-Phe5, D-Trp7,9, Leu11] substance P (D-Phe5SP) significantly inhibited DNA synthesis by 10/10 human tumour CLs; six SCLC, one N-SCLC (squamous), two ovarian and one squamous cervical carcinoma, with inhibition to 50% control levels (IC50) of 20-50 microM. There was dose dependent inhibition of colony forming efficiency (CFE) in 3/3 SCLC and 1/1 N-SCLC CL, IC50s of 0.5-6.5 microM in 5% serum. Exposure of SCLC CL HC12 to 100 microM D-Phe5SP for 1-4 h caused a progressive fall in viable cell number; surviving cells, grown in the absence of peptide, showed a decreased growth rate. During 1 week's exposure of two SCLC CLs to 20 microM D-Ph5SP, growth was slower than control cultures, while 50-100 microM completely inhibited growth. These inhibitory effects were partially reversed by increasing serum concentration from 5 to 20%, but not by SP, vasopressin, bombesin or insulin-like growth factor 1. There was some inhibition of CFE by 3/3 normal human bone marrows, IC50s of 30-80 microM, compared with 8 microM for HC12 in 20% FCS. Therefore D-Phe5SP appears to have more potent antiproliferative effects in tumour cells than normal cells, suggesting a role for this analogue in tumour treatment.

Dose-related involvement of CCK in bombesin-induced pancreatic growth

We examined the role of CCK in bombesin-induced pancreatic growth in rats using the CCK receptor antagonist L-364,718. Rats (155 +/- 1 g, 8-10 per group) received subcutaneous injections every 8 h for 5 days with bombesin (0.6, 1.7 and 5 nmol/kg) or bombesin in combination with L-364,718 (1 mg/kg). After 5 days the pancreas was removed and pancreatic weight, protein content, DNA, amylase and chymotrypsin contents were determined. Bombesin produced a significant increase (48-475%) of pancreatic weight, tissue contents of protein, DNA, amylase and chymotrypsinogen (F = 82, P less than 0.001). When a large dose of bombesin (5 nmol/kg) was combined with L-364,718 a significant inhibition (up to 70%) of all tissue parameters was observed (P less than 0.001). L-364,718 did not affect the growth response to a small dose of bombesin (0.6 nmol/kg). Plasma CCK levels 15 min after a single injection of bombesin (0.6, 1.7 and 5 nmol/kg) were significantly increased in response to the 5 nmol/kg dose (2.0 +/- 0.7 to 3.4 +/- 0.8 pM, F = 6.9, P less than 0.01). No increases of CCK plasma levels were found in response to the 0.6 and 1.7 nmol/kg doses of bombesin, corresponding to the lack of effects of L-364,718 on growth parameters at these doses. Measuring the time-course of CCK plasma levels after a single injection of 5 nmol/kg bombesin revealed an increase from basal values of 1.4 +/- 0.3 pM to maximal levels of 3.5 +/- 0.5 pM after 15 min (F = 7.1, P less than 0.001). Values returned to basal after 60 min. These results suggest that low doses of bombesin act directly at the acinar cell or through release of non-CCK growth factors whereas high doses of bombesin act in part through CCK release.

Effects of bombesin on pancreatic digestive enzyme gene expression

We examined the effects of bombesin on rat pancreatic digestive enzyme gene expression using cloned complementary DNA probes for amylase, trypsinogen I, chymotrypsinogen B, and lysophospholipase. Rats were injected sc three times daily with 5 nmol/kg body wt bombesin. Pancreata were investigated after 6, 12, 24, 48, and 120 h of hormone treatment. Bombesin administration resulted in a time-dependent increase of pancreatic weight, as well as DNA and protein concentration. Cellular hypertrophy became evident after 48 h, and pancreatic hyperplasia occurred after 5 days of hormone treatment. Bombesin administration resulted in a time-dependent parallel decrease of amylase and lysophospholipase messenger RNA (mRNA) concentrations with maximal inhibition occurring after 120 h of bombesin treatment (13 +/- 1% and 14 +/- 3% of control, respectively, P less than 0.05, n = 6). In contrast, chymotrypsin and trypsin mRNA levels remained unaltered after bombesin treatment for up to 5 days. Amylase and chymotrypsin enzyme levels did not correlate with their respective mRNA concentrations. Both decreased to approximately 50% of control after 12 h and increased to 126 +/- 38% of control and 388 +/- 109% of control (P less than 0.05, n = 6), respectively, after 5 days of bombesin treatment. To test whether the bombesin regulation was mediated by the release of cholecystokinin (CCK), the specific CCK receptor antagonist L-364,718 (1 mg/kg body wt) was injected ip either alone, or 15 min before each bombesin injection for 5 days. Although the antagonist alone significantly reduced the mRNA concentrations for trypsin, chymotrypsin, and lysophospholipase to approximately 50%, it did not block the effects of bombesin on pancreatic digestive enzyme levels. These data therefore indicate that bombesin regulates pancreatic digestive enzyme mRNA and protein concentrations in a nonparallel manner; furthermore, CCK is not involved in mediating the bombesin effects on pancreatic gene expression.

Inhibition of growth of PC-82 human prostate cancer line xenografts in nude mice by bombesin antagonist RC-3095 or combination of agonist [D-Trp6]-luteinizing hormone-releasing hormone and somatostatin analog RC-160

The effects of treatment with a bombesin receptor antagonist [D-Tpi6, Leu13 psi (CH2NH) Leu14]BN(6-14)(RC-3095) and the combination of an agonist of luteinizing hormone-releasing hormone [D-Trp6]-LH-RH and somatostatin analog D-Phe-Cys-Tyr-D-Trp-Lys-Val- Cys-Trp-NH2 (RC-160) were studied in nude mice bearing xenografts of the hormone-dependent human prostate tumor PC-82. During the 5 weeks of treatment, tumor growth was decreased in all treated groups compared with controls. Bombesin antagonist RC-3095 and the combination of [D-Trp6]-LH-RH and RC-160 caused a greater inhibition of tumor growth than [D-Trp6]-LH-RH or RC-160 alone as based on measurement of tumor volume and percentage change in tumor volume. The largest decrease in tumor weight was also seen in the groups treated with the bombesin antagonist and with the combination of RC-160 and [D-Trp6]-LH-RH. Serum prostatic-specific antigen levels were greatly decreased, and insulin-like growth factor I (IGF-I) as well as growth hormone levels were reduced in all treated groups. Specific binding sites for [D-Trp6]-LH-RH, epidermal growth factor (EGF), IGF-I, and somatostatin (SS-14) were found in the tumor membranes. Receptors for EGF were significantly down-regulated by treatment with the bombesin antagonist or RC-160. Combination of LH-RH agonists with somatostatin analog RC-160 might be considered for improvement of hormonal therapy for prostate cancer. The finding that bombesin antagonist RC-3095 inhibits the growth of PC-82 prostate cancer suggests the merit of further studies to evaluate the possible usefulness of antagonists of bombesin in the management of prostatic carcinoma.

Present status of agonistic and antagonistic analogs of LH-RH in the treatment of advanced prostate cancer

The methods for treatment of advanced prostate cancer, based on the agonistic analogs of LH-RH were reviewed. New therapeutic approaches utilizing antagonistic analogs of LH-RH such as SB-75 (Cetrorelix) have been described. Analogs of LH-RH chemically linked to various cytotoxic radicals are also being developed. Combinations of LH-RH agonists or antagonists with superactive somatostatin analogues such as Octastatin (RC-160) or with bombesin/GRP antagonists are being investigated in order to delay or prevent the relapse and improve the therapy for prostate cancer.

Characterization of the enhanced responsiveness to postingestive satiety signals in 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-treated Han/Wistar rats

Previous studies have shown that under free-feeding conditions, TCDD-treated Han/Wistar (H/W) rats consume less sucrose solution but ingest more saccharin solution than their controls thus implying hyperresponsiveness to postingestive satiety signals. In this study, nutrient preloads were employed to further elucidate this phenomenon. Male H/W rats were given a single high but usually non-lethal intraperitoneal dose (1000 micrograms/kg) of TCDD. Feed intake was stimulated by 24 hr feed deprivation at various time points after TCDD exposure. When TCDD-dosed rats were allowed to drink either a 20% sucrose or a 0.25% saccharin solution and then given access to feed, those that had had sucrose ate only about 50% of the amount consumed by the saccharin group. Although the preloads were similar in control rats, no such difference in subsequent feeding occurred. The sucrose solution also produced a longer-lasting suppression of feed intake in TCDD-treated compared with control rats when infused directly into the stomach. By contrast, TCDD-treated H/W rats failed to exhibit an augmented satiety response to parenterally applied glucose independent of testing time. Oral corn oil reduced feed intake in both control and TCDD-exposed rats, but the inhibition was slightly larger in TCDD-treated animals. TCDD did not markedly affect the responsiveness of H/W rats to the suppression of feeding by CCK-8 or bombesin. It is concluded that gastrointestinal factors appear critical to the exaggerated response of TCDD-treated H/W rats to nutrient energy.

Activation of tuberoinfundibular and tuberohypophysial dopamine neurons following intracerebroventricular administration of bombesin

The effect of bombesin on the activity of dopamine (DA) neurons comprising the nigrostriatal, mesolimbic, tuberoinfundibular and tuberohypophysial systems in the male rat was determined by measuring: (1) the accumulation of 3,4-dihydroxyphenylalanine (DOPA) after administration of a decarboxylase inhibitor, and (2) the concentration of the DA metabolite 3,4-dihydroxyphenylacetic acid (DOPAC) in brain (striatum, nucleus accumbens, median eminence) and pituitary regions (intermediate and neural lobes) containing terminals of these neurons. Intracerebroventricular (i.c.v.) injection of bombesin caused a dose- and time-related increase in the activity of DA neurons projecting to the median eminence and intermediate lobe of the pituitary, and a corresponding decrease in the concentrations of prolactin and alpha-melanocyte-stimulating hormone (alpha MSH) in the plasma. In contrast, doses of bombesin up to 10 ng i.c.v. failed to alter the activity of DA neurons terminating in the striatum, nucleus accumbens or neural lobe of the pituitary gland. Equimolar doses of bombesin and gastrin-releasing peptide (GRP), a bombesin-like peptide, increased the concentrations of DOPAC in the median eminence and intermediate lobe of the pituitary, suggesting that GRP-preferring receptors may be responsible for the stimulatory effects of bombesin on DA neuronal activity in these regions. The results of these studies suggest that bombesin increases the activity of tuberoinfundibular and tuberohypophysial DA neurons projecting to the median eminence and intermediate lobe of the pituitary, respectively, and thereby inhibits the secretion of prolactin and alpha MSH.

Bombesin effects on responding maintained by a fixed interval schedule of food reinforcement

The present experiment examined rats' responding maintained by a fixed interval two-min schedule of food reinforcement following IP injections of bombesin (4, 6, 16, 32 micrograms/kg). The results showed that bombesin's effects were rate dependent where the responses per minute emitted during the early portion of the fixed interval were reduced, but responding during the latter portion was unaffected. Bombesin did not reduce overall session responses per minute, pause after reinforcement, or amount of water consumed in the test chamber. The results are in accord with prior research examining the effects of bombesin and cholecystokinin on operant behavior. Together, the data challenge the notion that bombesin affects food-motivated behavior generally; rather, the results indicate that bombesin's effect may interact with the demands required of the animal for reinforcement.

Effects of fourth ventricle bombesin injection on meal-related parameters and grooming behavior

Injections of bombesin (BN) into the vicinity of the caudal brainstem suppress food intake in rats. In the present study, the food intake parameters [meal size (MS), intermeal interval (IMI), satiety ratio (SR)] affected by 4th ventricle BN injections were determined. Following a 15-h food deprivation, rats were administered 4th ventricle injections of saline (0.15 M) and BN in doses of 1, 5, 10, and 20 ng BN, and were then given access to sweetened milk. The animals' behaviors (feeding, resting, grooming, exploring) were scored every one min and milk intake every five min for 60 min following the injections. Fourth ventricle injections of 5 ng BN and greater reliably suppressed milk. intake. This reduction was reflected in a significant reduction in the MS. The IMI was not affected. As a result, the SR (IMI2/MS1), which is thought to represent the satiating property of food, was reliably greater following BN than following saline administration. The reduced food intake was accompanied by a significant increase in grooming behavior and a corresponding decrease in exploring. The amount of time spent resting (inactive) was similar following saline and all but the highest dose of BN. To demonstrate that the behavioral effects of BN were mediated by specific caudal brainstem BN receptors, 4th ventricle injections of [D-Phe12,Leu14]BN, a BN receptor antagonist, or saline preceded the 4th ventricle injection of 5 ng BN. Pretreatment with [D-Phe12,Leu14]BN reliably blocked the effects of BN on food intake and grooming.

Aging and the trophic effects of cholecystokinin, bombesin and pentagastrin on the rat pancreas

We examined the effect of age on the trophic response of the pancreas to chronic treatment with cholecystokinin (CCK), bombesin, or pentagastrin. Three age groups (3-, 12-, and 24-months) male F344 rats received saline; CCK-8 (5 ng/kg), bombesin (10 micrograms/kg), or pentagastrin (100 micrograms/kg) by intraperitoneal injection t.i.d. for 2 weeks. Rats were then killed and the pancreases excised, weighed, and assayed for DNA, RNA, protein, and polyamine (putrescine, spermidine, and spermine) concentrations and contents. We found that none of the treatments altered body weight at any age. All three hormones increased pancreas size and cell number in 3-month old rats, but by 12 months, all three had increased only pancreatic RNA content. Pancreatic spermidine concentration was decreased by all three hormone regimens in 3- but not in 12-month old rats, and pancreatic putrescine concentration and content were increased in 12-month old rats receiving all three hormones. There was no change in any parameter following any of the three hormones, tested at 24 months of age. We conclude that, at the dosages tested, the trophic response of pancreas to chronic administration of CCK, bombesin, and pentagastrin, which is normally present in young adult rats, is lost with aging.

N-acetyl-GRP(20-26)-O-CH3 reverses intracisternal bombesin-induced inhibition of gastric acid secretion in rats

Intracisternal injection of 19 pmoles of bombesin in light-ether-anesthetized rats, five minutes after intracisternal vehicle, produced a 75% and 63% inhibition in gastric acid output and concentration, respectively, in 2-hour pylorus-ligated rats. Pretreatment of rats with the characterized peripheral bombesin antagonist N-acetyl-GRP(20-26)-O-CH3 (1 nmole) reversed the inhibitory effect of bombesin on gastric acid output and concentration. In contrast, the related bombesin antagonist N-acetyl-GRP-O-CH2-CH3 (1 nmole) was ineffective in this system. In urethane-anesthetized, acute gastric fistula rats infused with pentagastrin, intracisternal N-acetyl-GRP(20-26)-O-CH3 protected against the inhibition in gastric acid output produced by intracisternal bombesin (19 pmoles). Thus the recently characterized peripheral bombesin antagonist N-acetyl-GRP(20-26)-O-CH3 also appears to be effective in antagonizing central bombesin-induced inhibition in gastric acid secretion in two models. This represents a first report of a synthetic bombesin antagonist effective in reversing central bombesin-induced effects on gastric function.

Bombesin differentially affects gastric emptying in suckling, weanling and adult rats

The gastric effect of bombesin, a homolog of the mammalian peptide found in breast milk, was studied in suckling, weanling and adult rats (11, 30 and 90 days old, respectively). Control gastric emptying was not different in the three age groups. When bombesin was given orogastrically in a saline vehicle, 30 min before a nonabsorbable radiolabeled marker (used to assess gastric emptying), a significant and dose-related inhibitory effect was observed in sucklings. In contrast to the data with orogastric peptide in saline, when bombesin was given orogastrically in rat milk 30 min before the marker, there was no effect on gastric emptying in sucklings. Inhibition of gastric emptying was again demonstrated in the sucklings when bombesin (0.6-30 micrograms) was given with an artificial rat milk substitute 30 min before the marker. In contrast, orogastric bombesin in rat milk or rat milk substitute had no effect on gastric emptying in weanlings or adults. While s.c. bombesin in saline did not alter gastric emptying in sucklings, s.c. administration of the peptide produced a significant and dose-related increase in gastric emptying in both weanlings and adults. These results support the concept that milk-borne peptides, such as gastrin releasing peptide, may be involved in regulation of gastric function in suckling rats.

Central nervous system site of action of bombesin to elevate plasma concentrations of catecholamines

To identify the central nervous system site of action of bombesin to elevate plasma concentrations of catecholamines, this peptide has been injected into numerous brain ventricular and parenchymal sites. Low doses of bombesin (1-10 ng) injected into the region of the rostral nucleus tractus solitarius (NTS) elicited an elevation of plasma catecholamines greater than those observed following an injection of bombesin into other brain regions. Bombesin-induced (10 ng) elevation of plasma epinephrine but not norepinephrine was prevented by co-administration of somatostatin-28 (100 ng). Mean arterial pressure (MAP) and heart rate (HR) were measured following injection of bombesin into the NTS. Bombesin injected into the NTS resulted in prolonged decreases in HR without significantly altering MAP. These studies demonstrate that bombesin injected into the dorsal medulla resulted in significant changes of plasma catecholamine levels and HR. Based on these actions of bombesin and the neuroanatomic distribution of bombesin-like peptide, it is suggested that this peptide may play an important role in regulation of sympatho-adrenal and cardiac functions.

Chemical sympathectomy with 6-hydroxydopamine potentiates intracerebroventricularly applied bombesin-induced increase in plasma adrenaline

Intracerebroventricular administration of bombesin induced a marked increase in plasma level of adrenaline and a slight increase in that of noradrenaline in rats anesthetized with urethane. The bombesin-induced increase in adrenaline was potentiated by chemical sympathectomy with 6-hydroxydopamine (6-OHDA). On the other hand, adrenalectomy did not affect plasma level of noradrenaline in the bombesin-treated animals. In the splanchnicotomized rats, direct stimulation of the adrenal glands by intravenously administered nicotine increased plasma level of both adrenaline and noradrenaline. These increases were, however, not potentiated by chemical sympathectomy with 6-OHDA. Pretreatment with capsaicin, a potent toxin selective to sensory neurons, potentiated the bombesin-induced increase in plasma level of adrenaline. In these capsaicin pretreated rats, chemical sympathectomy did not potentiate the bombesin-induced increase in plasma level of adrenaline to any great extent. These results suggest that chemical sympathectomy with 6-OHDA potentiated the bombesin-induced increase in plasma adrenaline probably due to a disinhibitory activation of the splanchnic nerve by as yet unidentified but capsaicin sensitive neuron mechanisms.

Effects of dopamine D1 and D2 receptor agonists and antagonists on bombesin-induced behaviors

Central administration of bombesin elicits excessive grooming and locomotor activity in rats. This grooming activity is one characterised by vigorous scratching of the face, nape and body flanks. Pretreatment with the D1 receptor antagonist SCH 23390 inhibited the expression of bombesin-induced activity with grooming being more inhibited than locomotion. Blockade of D2 receptors with eticlopride significantly attenuated the behavioral responses to bombesin. When SCH 23390 and eticlopride were administered concurrently, it was apparent that D1 blockade had a greater effect on grooming and D2 blockade a larger effect on locomotion. Stimulation of D1 receptors by SKF 38393 elicited non-stereotyped locomotor activity and a form of grooming behavior characterised by vigorous washing of the face and ventral body surfaces. Co-administration of bombesin and SKF 38393 resulted in a form of grooming which resembled that elicited by SKF 38393 alone. The specific D2 agonist PPHT elicited a form of locomotion characterised by a downward oriented head posture and slow ambulatory activity around the cage perimeter. Co-administration of PPHT and bombesin resulted in a complete suppression of bombesin-induced behaviors and was largely indistinguishable from activity observed under PPHT alone conditions. These data implicate both D1 and D2 receptor based mechanisms in the modulation/mediation of the behavioral effects of bombesin. Part of the bombesin-induced behavioral effects may be explained by (indirect) activation of (a) dopamine system(s).

Aversive properties of bombesin in rats

Aversive properties of bombesin were determined in the conditioned place-preference paradigm in rats and compared with the effects on spontaneous behavior. Bombesin induced excessive grooming and/or scratching behavior at doses of 80 ng, 400 ng, and 2.0 micrograms ICV. In the conditioned place-preference paradigm, doses of 400 ng and 2.0 micrograms ICV induced a profound aversion to the environment in which the animals had received peptide treatment. Eighty ng were partially effective, and 16 ng did not induce a significant change in preference. The grooming/scratching behavior was attenuated by pretreatment with 4 mg/kg morphine-sulfate. These results show that bombesin is strongly aversive at doses that induce grooming/scratching behavior. Although the relationship between these different effects is not known, the similarity in their dose-response relationship suggests that they may be mediated by a common mechanism.

[The effect of microinjections of bombesin into the amygdala on the slow-wave frequency of the gastroduodenal smooth muscles and on the migrating myoelectric complex]

In dogs with electrodes implanted in the smooth muscle wall of the stomach and duodenum, microinjection of bombesin (5 micrograms) during the 2nd phase of the migrating myoelectric complex decreased frequency of slow waves in the stomach, leaving unaltered the frequency of slow waves in the duodenum. Bombesin caused a short-term inhibition of the gastric and intestinal spike activity followed by its increase, the active period of the migrating myoelectric complex being prolonged.

Bombesin potentiates the effect of acetylcholine on isolated strips of fish stomach

The interaction between bombesin and acetylcholine acting on smooth muscle of the stomach wall was investigated in two species of teleost fish. Oncorhynchus mykiss (rainbow trout) and Gadus morhua (Atlantic cod). Acetylcholine or bombesin alone has an excitatory effect on the stomach muscle. The effect on contraction amplitude of acetylcholine (10(-6)-10(-5) M) alone is about 10-times greater than the effect of bombesin (10(-9)-10(-7) M). In molar terms however, bombesin is more potent than acetylcholine. Bombesin (10(-8)-10(-7) M) added 0.5-3 min prior to acetylcholine potentiates the effect of acetylcholine in a dose-dependent manner. The potentiation is most pronounced in circular muscle preparations, but is present also in longitudinal muscle preparations. Bombesin affects the response to carbachol (10(-6) M) with a similar potentiation, indicating that the potentiation is not caused by inhibition of choline esterase activity. Atropine (10(-6)-10(-5) M) abolishes the response to bombesin plus acetylcholine as well as the response to acetylcholine alone. Tetrodotoxin (10(-6) M) does not block the effect of acetylcholine, bombesin or the combination acetylcholine plus bombesin. Substance P (10(-9)-10(-7) M) which has a similar excitatory effect on the stomach muscle as bombesin, does not potentiate the effect of acetylcholine. Immunohistochemistry has shown the presence of strong bombesin-like immunoreactivity in stomach nerves of the cod and weak bombesin-like immunoreactivity in rainbow trout nerves. In addition, bombesin-like immunoreactivity was demonstrated in endocrine cells in the gastric and intestinal mucosa of both species. It is concluded that bombesin, contained either in nerve fibres or in mucosal endocrine cells, specifically potentiates the effect of acetylcholine in the fish stomach.

Microinfusion of bombesin into the hypothalamic paraventricular nucleus produces hypothermia in the insulin-pretreated rat

Bombesin-like peptides are widely distributed in the mammalian central nervous system and participate in the regulation of a variety of autonomic functions. Central injection of bombesin produces hypothermia at normal ambient temperatures, but only if the rat has been food-deprived or made hypoglycemic with insulin. Two experiments were conducted to reevaluate the impact of bombesin microinfusion into the hypothalamic paraventricular nucleus (PVN) on core body temperature and feeding behavior. In Experiment 1, bombesin (0.05 and 0.1 microgram/1.0 microliter) produced hypothermia, but not hypophagia, in rats (n = 5) pretreated with insulin (10 U/kg; IM). Since a similar response was observed in rats with injection sites adjacent to the PVN, a smaller injection volume was evaluated in Experiment 2. Hypothermia, but not hypophagia, was observed in rats (n = 5) pretreated with insulin following bombesin (0.025 and 0.05 micrograms/0.5 microliter). Bombesin did not produce hypothermia in rats with injection sites outside of the PVN. These findings suggest that the PVN is a sensitive site for bombesin-induced hypothermia.

Effects of prolonged administration of neurotensin, arginine-vasopressin, NPY, and bombesin on blood TSH, T3 and T4 levels in the rat

Adult female rats were i.p. infused (Alzet osmotic minipumps) with neurotensin (NT, 2 micrograms/rat/day for 7 days), arginine-vasopressin (AVP, 2 micrograms/rat/day for 8 days), bombesin (BM, 0.75 microgram/rat/day for 7 days) or injected with neuropeptide Y (NPY, 0.5 microgram/rat twice a day for 4 days). NT infusion increased absolute and relative thyroid gland weight and decreased serum T4 level, while serum TSH and T3 levels remained unchanged. AVP treatment increased thyroid gland weight and serum TSH and T4 levels and a similar effect was induced by prolonged BM infusion. On the other hand, NPY administration had no effect either on thyroid gland weight or on serum TSH, T4 and T3 levels. Results of the present study thus clearly demonstrate a potent stimulatory action of AVP and BM on thyroid gland function and suggest that this effect is mediated by the pituitary gland. On the contrary, prolonged NT infusion decrease serum T4 level while NPY had no effect on thyroid gland function.

The effects of intraventricular injections of bombesin on temperature selection in the rat

The purpose of these experiments was to elucidate further the possibility that intraventricular injections of bombesin (BBS) lower the set point around which an animal regulates its core body temperature. In an attempt to prevent a confounding of general activity and thermoregulatory behavior which occurred in earlier work, a horizontal temperature gradient was used. Intraventricular injections of bombesin resulted in the selection of temperatures that were approximately 9-13 degrees C colder than those selected by animals following control injections. Additionally, the increase in core body temperature observed following control injections was reversed by the highest dose of bombesin. No significant alterations in general locomotor activity were observed. These findings suggest that bombesin may act centrally to reduce the set point around which behavioral responses are regulated.

Changes in gastric secretion after intracerebroventricular infusion of bombesin in dogs

Synthetic bombesin (BBS) was infused intracerebroventricularly in 14 mongrel dogs, to study the effects of the peptide on gastric secretion and on gastrin and neurotensin levels. The infusion was performed with a specific apparatus, and gastric fluid was collected with a Pavlov pouch. BBS was given in two series of experiments: as a bolus intracerebroventricular injection of 308.6 pmol/kg and as a continuous intracerebroventricular infusion at a rate of 617.3 pmol/kg/h for 30 min. The bolus injection caused a very significant decrease of gastric fluid volume, a significant decrease of HCl output, and a significant increase of its pH, while serum immunoreactive gastrin increased significantly. The continuous infusion of BBS caused similar changes in gastric secretion. The plasma neurotensin levels did not change. In conclusion, the intracerebroventricular administration of BBS increases the serum gastrin levels, decreases the volume and HCl content of gastric fluid, and increases its pH.

Role of gastrin and cholecystokinin in the growth-promoting action of bombesin on the gastroduodenal mucosa and the pancreas

The effects of bombesin on the growth of the gastroduodenal mucosa and the pancreas have been examined in adult rats with intact or resected antrum and following administration of somatostatin or CCK-receptor antagonist L-364,718. The peptides were administered three times daily for 7 consecutive days, and then the animals were sacrificed and growth parameters (organ weight and RNA and DNA contents) were determined, and plasma gastrin and CCK were assayed. Compared with the control (saline) values, bombesin significantly stimulated the growth of the oxyntic and duodenal mucosa and the pancreas. These effects were partly reduced but not abolished by somatostatin, antrectomy and L-364,718, suggesting that bombesin may enhance the growth partly by releasing gastrin and CCK and partly by direct action on these tissues.

Intake of individual macronutrients following IP injections of BBS and CCK in rats

The effects of injections of either bombesin (BBS) or cholecystokinin octapeptide (CCK-8) on patterns of food intake of macronutrients were examined in adult male rats, and compared to the effects following saline injections. The animals were food deprived for 18 hours and then offered one of three isocaloric dietary components (protein, carbohydrate or fat). During the first 30 minutes following injections of BBS, protein intake was decreased. Suppression of carbohydrate intake, significant between 30 and 60 minutes, was sustained up to two hours following injections. During the first 30 minutes following injections of CCK, animals reduced their intake of each macronutrient. Reductions in the consumption of fat and protein were sustained up to one and six hours, respectively. The availability of particular macronutrients is proposed as a possible factor accounting for differences among studies with respect to self-selection profiles and duration effects.

Effect of antibodies to the neuropeptide GRP on distention-induced gastric acid secretion in the rat

The present study examined and compared the effects of muscarinic blockade, beta-adrenergic blockade and immunoneutralization of the neuropeptide gastrin-releasing peptide (GRP) on distention-induced gastric acid secretion and gastrin release. In response to distention of rat stomachs with 0.9% NaCl, acid output rose from 3.5 +/- 0.5 mumol H+/30 min to 15.4 +/- 2.5 mumol H+/30 min (P less than 0.01). Intravenous administration of 4 mg/kg propranolol did not affect the acid secretory response to distention, however both 2 mg/kg atropine and 6 mg/kg pirenzepine significantly decreased gastric acid secretion by 44.8 +/- 7.8% and 40.9 +/- 5.7% (P less than 0.05), respectively. When specific antibodies to GRP were infused intravenously, the acid secretory response to distention was nearly abolished, decreasing to 5.1 +/- 0.8 mumol H+/30 min (P less than 0.01). In contrast to the effects on acid secretion, GRP antiserum did not significantly alter the gastrin release observed following distention. Results of these studies indicate that, under the conditions of these experiments, the acid secretory response to gastric distention may be independent of its effect on gastrin release. Although distention-induced gastric acid secretion may be partially governed by muscarinic pathways, the acid secretory response to distention in the rat appears to involve GRP-containing neurons.