Biology Reference
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tubules had a lumen and the gland substance was comprised of columnar cells. The
H. nasicus
gland was highly vascular and had serous as well as mucous cells, while that
of
H. platirhinos
was moderately vascular and lacked mucous cells. Neither species pos-
sessed mucous supralabial glands associated with their Duvernoy's glands (Taub, 1967).
In comparison, Fry et al. (2008) reported that both species exhibited glandular epithelium
with mucous cells or patches and a “venom duct” that opened only into the oral cavity,
not into the vicinity of any specific dentition. The diameter of the duct appeared reduced
and surrounded by circular connective tissue (Fry et al., 2008).
4.2.4.2 Summary of the Toxinology and Duvernoy's Secretion Properties of
Heterodon
spp.
The scarce data regarding yield of Duvernoy's secretion from
Heterodon
spp. indi-
cate limited average volumes from a small series of specimens. Mean liquid yields
from two specimens each of
H. nasicus nasicus
and
H. n. kennerlyi
(Mexican hog-
nose,
H. kennerlyi
; Smith et al., 2003) were 24 and 15 μL, respectively (Hill and
Mackessy, 2000).
There are few data regarding components of Duvernoy's secretions from
Heterodon
spp. Hill and Mackessy (2000) found low phosphodiesterase, moderate-
to-high proteolytic activity, but no PLA
2
activity in
H. nasicus
Duvernoy's secretion.
They found that enzymatic constituents of
Heterodon
spp. saliva and Duvernoy's
secretions differed. Saliva from the nominate form,
H. n. nasicus
, lacked proteolytic
activity and exhibited high levels of PLA
2
(Hill and Mackessy, 2000). None of the
Heterodon
spp. secretions studied contained detectable thrombin-like, hyaluronidase,
or kallikrein-like activities (Hill and Mackessy, 2000).
As noted with
Boiga
spp., the
in vitro
detection of postsynaptically active neuro-
toxins present in Duvernoy's secretions from
H. platirhinos
(Young, 1992) appears
to be irrelevant to elucidating the basis for the observed clinical effects of bites from
this species. Young (1992) reported induction of acetylcholinesterase-like neuro-
muscular blockade by
H. platirhinos
Duvernoy's secretion in the frog sciatic nerve-
gastrocnemius preparation, as well as antagonism of acetylcholine and histamine
responses of isolated rat duodenum. It is likely that many of these toxins are prey
(anuran amphibians) specific, following preferences of these snakes, although
H.
nasicus
readily preys upon small mammals.
4.2.4.3 Conclusion and Assessment of
Heterodon
spp.
Well-documented bites from
Heterodon
spp. (almost all from
H. nasicus
) feature
mild-to-moderate local effects including puncture wounds/lacerations, mild-moder-
ate edema, blistering, ecchymoses and, uncommonly, mild lymphadenopathy (
Table
4.1
). Several reports describe extended convalescence (weeks to months) of patients
after protracted bites from these snakes. However, as with
Thamnophis
spp., despite
the many thousands of these snakes kept in captivity, bites and local “envenomations”
are exceedingly rare. This genus does not deserve to be considered venomous or
