Expression of prepro-VIP derived peptides in the gastrointestinal tract of normal, hypothyroid and hyperthyroid rats

VIP and PACAP

Vasoactive intestinal polypeptide (VIP) is derived from a 170 amino acid precursor which in addition is processed to preproVIP 22-79, PHI, preproVIP 111-122 and preproVIP 156-170. All preproVIP-derived peptides have been shown in normal tissue and VIP-producing cell lines and elevated quantities occur in plasma and tumour tissues from patients with VIP-producing tumours. In some tissues the dibasic cleavage site after PHI is uncleaved resulting in a C-terminally extended form, PHV. PHI and VIP are present in a 1:1 molar ratio in large dense core vesicles and released in roughly equimolar amounts. Carboxyamidation of VIP and PHI is not critical and glycine-extended forms of both peptides have been demonstrated. Pituitary adenylate cyclase activating polypeptide (PACAP) is derived from a 170 amino acid long precursor, which gives rise to PACAP 38, PACAP 27 and PACAP related peptide (PRP). All peptides are present in tissue, the dominating form being PACAP 38. Prohormone convertase (PC) 1 and 2 seem to be involved in the processing of PACAP, except in the testes and ovary, where the PACAP precursor is substrate for PC4.

Neurotransmitters co-existing with VIP or PACAP

It is now recognized that a neuron can produce, store and release more than one transmitter substance, and a number of examples of co-existing transmitters, particularly a neuropeptide together with a classical transmitter, have been reported. The present paper deals with transmitter substances, peptides or classical transmitters, co-existing with the two structurally related peptides VIP and PACAP and the possible functional implications of this co-existence.

Identification of a potential receptor for both peptide histidine isoleucine and peptide histidine valine

Peptide histidine isoleucine (PHI), peptide histidine valine (PHV), and vasoactive intestinal polypeptide (VIP) are cosynthesized from the same precursor and share high levels of structural similarities with overlapping biological functions. In this study, the first PHI/PHV receptor was isolated and characterized in goldfish. To study this receptor using homologous peptides, we have also characterized the goldfish prepro-PHI/VIP, and, surprisingly, a shorter transcript lacking the VIP coding region was isolated. A PHI/VIP precursor without the VIP coding sequence has never before been reported. Initial functional expression of the PHI/PHV receptor in Chinese hamster ovary cells revealed that it could be activated by human PHV [50% effective concentration (EC(50)): 43 nM] and to a lesser extent human PHI (EC(50): 133 nM) and helodermin (EC(50): 166 nM) but not fish and mammalian pituitary adenylate cyclase-activating polypeptides and VIPs. Subsequent studies indicated that, similar to the pituitary adenylate cyclase-activating polypeptide receptors (PAC1-R, VPAC1-R, and VPAC2-R), the receptor isolated in this study is able to interact with goldfish PHI and its C-terminally extended form, PHV with EC(50) values 93 and 43 nM, respectively. Northern blot and RT-PCR/Southern blot analyses revealed that the PHI/VIP gene is expressed in the intestine, brain, and gall bladder and the PHI/PHV receptor gene is primarily expressed in the pituitary and to a lesser extend in the intestine and gall bladder, suggesting that PHI/PHV may play a role, notably in the regulation of pituitary function. In conclusion, our results demonstrate for the first time the existence of a PHI/PHV receptor, indicating that the functions of PHI and PHV could be mediated by their own receptor in addition to VIP receptors.

Colocalization of VIP with AVP in neurons of the human paraventricular, supraoptic and suprachiasmatic nucleus

Aim of this study was to investigate, with the aid of a recently developed immunofluorescence technique, cellular colocalization of vasoactive intestinal peptide (VIP) with arginine-vasopressin (AVP) in the paraventricular nucleus (PVN), the supraoptic nucleus (SON) and the suprachiasmatic nucleus (SCN) of the human hypothalamus. To this end, six hypothalami resected from patients who had died suddenly served as material of research. After formaldehyde fixation and subsequent storage in 30% sucrose, 25-microm thick cryosections were cut of one half of each hypothalamus. These sections were double-immunolabeled with primary antibodies against AVP and VIP followed by fluorophore-conjugated secondary antibodies. Autofluorescence, mainly caused by lipofuscin granules in neurons and glial cells, was blocked by a specially developed procedure consisting of incubating the immunolabeled sections in a Sudan Black B solution. Quantitative analysis with a confocal laser scanning microscope showed that of all stained cellular profiles the percentages of profiles immunoreactive exclusively for AVP or VIP or for both neuropeptides (colocalization) were for the SCN approximately 76.5%, 19.6% and 3.9%, for the SON 97.7%, 0.2% and 2. 1% and for the PVN 93.2%, 1.6% and 5.2%, respectively. These data illustrate that colocalization between AVP and VIP is not only present in neurons of the PVN and SON, but also in neurons of the SCN. This unexpected finding illustrates that the human SCN may also use a highly differentiated language to transmit its circadian signal to the rest of the brain.

Anorectal physiology and transit in patients with disorders of thyroid metabolism

BACKGROUND

Data on anorectal physiology in patients with disordered thyroid metabolism are lacking. This prospective study was performed to evaluate anorectal physiology in patients with either hyperthyroidism and diarrhoea, or hypothyroidism and constipation in order to assess slow transit in hypothyroid patients.

METHODS

Thirty patients with hypothyroidism and constipation (24 females, median age 59 years, range 23-80) and 20 patients with hyperthyroidism and diarrhoea (12 females, median age 46 years, range 36-62) were evaluated by anal manometry, rectal balloon sensation and whole-gut transit markers. Data were compared with anorectal physiology and whole-gut transit in 22 healthy controls (13 females, median age 51 years, range 24-65).

RESULTS

In the hypothyroid patients, maximum resting pressure (MRP) and maximum squeeze pressure (MSP) were similar to controls (patients, median MRP 55 mmHg (18-98); controls, median MRP 41 mmHg (20-105) and patients, median MSP 83 mmHg (39-400); controls, median MSP 88 mmHg (30-230); P > 0.05 for both resting and squeeze pressures). In hyperthyroid patients, median MRP and MSP were significantly lower than controls (patients, MRP 33 mmHg (8-69); controls MRP 41 mmHg (20-105) P = 0.04 and patients, MSP 60 mmHg (26-104); controls, MSP 88 mmHg (30-230); P = 0.03). Threshold sensation for impending evacuation in hypothyroid patients was significantly higher than controls, while in hyperthyroid patients, threshold sensation was significantly lower compared with controls. Maximum tolerable rectal volumes in hypothyroid patients was significantly lower compared with controls, while no significant difference was found between maximum tolerable rectal volumes in hyperthyroid patients and controls. Prevalence of delayed whole-gut transit in both hypothyroid and hyperthyroid patients was similar to controls. Furthermore, 33% of hypothyroid patients and 40% of hyperthyroid patients experienced symptoms of bowel dysfunction prior to the onset of their thyroid disorder.

CONCLUSIONS

Patients with altered thyroid function and bowel dysfunction demonstrated abnormalities of anal manometry and rectal sensation.